diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f3eb3d6..1e9fd1f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         java: [11]
-        scala: [2.12.20, 2.13.15, 3.3.4]
+        scala: [2.13.15, 3.3.4]
         flink: [1.18.1, 1.19.1]
         include:
           - scala: 3.3.4
diff --git a/README.md b/README.md
index 88e7904..d5259bd 100644
--- a/README.md
+++ b/README.md
@@ -1,12 +1,12 @@
-# Scala 2.12/2.13/3.x API for Apache Flink
+# Scala 2.13/3.x API for Apache Flink
 
 [![CI Status](https://github.com/flink-extended/flink-scala-api/workflows/CI/badge.svg)](https://github.com/flinkextended/flink-scala-api/actions)
-[![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.flinkextended/flink-scala-api_2.12/badge.svg?style=plastic)](https://maven-badges.herokuapp.com/maven-central/org.flinkextended/flink-scala-api_2.12)
+[![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.flinkextended/flink-scala-api_2.13/badge.svg?style=plastic)](https://maven-badges.herokuapp.com/maven-central/org.flinkextended/flink-scala-api_2.13)
 [![License: Apache 2](https://img.shields.io/badge/License-Apache2-green.svg)](https://opensource.org/licenses/Apache-2.0)
 ![Last commit](https://img.shields.io/github/last-commit/flink-extended/flink-scala-api)
 ![Last release](https://img.shields.io/github/release/flink-extended/flink-scala-api)
 
-This project is a community-maintained fork of official Apache Flink Scala API, cross-built for scala 2.12, 2.13 and 3.x.
+This project is a community-maintained fork of official Apache Flink Scala API, cross-built for scala 2.13 and 3.x.
 
 ## Migration 
 
@@ -26,12 +26,12 @@ import org.apache.flinkx.api.serializers._
 
 ## Usage 
 
-`flink-scala-api` is released to Maven-central for 2.12, 2.13 and 3. For SBT, add this snippet to `build.sbt`:
+`flink-scala-api` is released to Maven-central for 2.13 and 3. For SBT, add this snippet to `build.sbt`:
 ```scala
 libraryDependencies += "org.flinkextended" %% "flink-scala-api" % "1.18.1_1.1.6"
 ```
 
-For Ammonite:
+## For Ammonite
 
 ```scala
 import $ivy.`org.flinkextended::flink-scala-api:1.18.1_1.1.6`
@@ -39,6 +39,22 @@ import $ivy.`org.flinkextended::flink-scala-api:1.18.1_1.1.6`
 import $ivy.`org.apache.flink:flink-clients:1.18.1`
 ```
 
+## For Scala 2.12
+
+If you want first to migrate to org.flinkextended:flink-scala-api staying on Scala 2.12, you can use the last build for Scala 2.12:
+
+```scala
+libraryDependencies += "org.flinkextended" %% "flink-scala-api" % "1.18.1_1.2.0"
+// or
+"org.flinkextended" %% "flink-scala-api" % "1.19.1_1.2.0"
+// or
+"org.flinkextended" %% "flink-scala-api" % "1.20.0_1.2.0"
+```
+
+Build for Scala 2.12 is no longer published.
+
+## SBT Project Template
+
 If you want to create new project easily check this __Giter8 template__ out: [novakov-alexey/flink-scala-api.g8](https://github.com/novakov-alexey/flink-scala-api.g8)
 
 ## Supported Flink versions
diff --git a/build.sbt b/build.sbt
index b054ea6..2690562 100644
--- a/build.sbt
+++ b/build.sbt
@@ -9,6 +9,7 @@ lazy val flinkVersion     = System.getProperty("flinkVersion", "1.18.1")
 lazy val root = (project in file("."))
   .aggregate(`scala-api`, `examples`)
   .settings(
+    scalaVersion   := rootScalaVersion,
     publish / skip := true
   )
 
@@ -17,7 +18,7 @@ lazy val `scala-api` = (project in file("modules/scala-api"))
   .settings(
     name               := "flink-scala-api",
     scalaVersion       := rootScalaVersion,
-    crossScalaVersions := Seq("2.12.20", "2.13.15", rootScalaVersion),
+    crossScalaVersions := Seq("2.13.15", rootScalaVersion),
     libraryDependencies ++= Seq(
       "org.apache.flink"  % "flink-streaming-java" % flinkVersion,
       "org.apache.flink"  % "flink-java"           % flinkVersion,
diff --git a/modules/scala-api/src/main/scala-3/org/apache/flinkx/api/TaggedDerivation.scala b/modules/scala-api/src/main/scala-3/org/apache/flinkx/api/TaggedDerivation.scala
index 8688333..c53decc 100644
--- a/modules/scala-api/src/main/scala-3/org/apache/flinkx/api/TaggedDerivation.scala
+++ b/modules/scala-api/src/main/scala-3/org/apache/flinkx/api/TaggedDerivation.scala
@@ -30,6 +30,7 @@ trait CommonTaggedDerivation[TypeClass[_]]:
       )*
     )
 
+    @annotation.nowarn
     val caseClass = new CaseClass[Typeclass, A](
       typeInfo[A],
       isObject[A],
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/ClosureCleaner.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/ClosureCleaner.scala
index 2426eae..8cabf98 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/ClosureCleaner.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/ClosureCleaner.scala
@@ -31,6 +31,7 @@ import org.slf4j.LoggerFactory
 
 import scala.collection.mutable
 import scala.jdk.CollectionConverters._
+import scala.annotation.tailrec
 
 /** A cleaner that renders closures serializable if they can be done so safely.
   */
@@ -63,20 +64,27 @@ object ClosureCleaner {
   // not a good idea (whereas we can clone closure objects just fine since we
   // understand how all their fields are used).
   private def getOuterClassesAndObjects(obj: AnyRef): (List[Class[_]], List[AnyRef]) = {
-    for (f <- obj.getClass.getDeclaredFields if f.getName == "$outer") {
-      f.setAccessible(true)
-      val outer = f.get(obj)
-      // The outer pointer may be null if we have cleaned this closure before
-      if (outer != null) {
-        if (isClosure(f.getType)) {
-          val recurRet = getOuterClassesAndObjects(outer)
-          return (f.getType :: recurRet._1, outer :: recurRet._2)
-        } else {
-          return (f.getType :: Nil, outer :: Nil) // Stop at the first $outer that is not a closure
-        }
+
+    @tailrec
+    def loop(fields: List[Field]): (List[Class[_]], List[AnyRef]) =
+      fields match {
+        case f :: tail =>
+          f.setAccessible(true)
+          val outer = f.get(obj)
+          // The outer pointer may be null if we have cleaned this closure before
+          if (outer != null) {
+            if (isClosure(f.getType)) {
+              val recurRet = getOuterClassesAndObjects(outer)
+              (f.getType :: recurRet._1, outer :: recurRet._2)
+            } else {
+              (f.getType :: Nil, outer :: Nil) // Stop at the first $outer that is not a closure
+            }
+          } else loop(tail)
+        case Nil => (Nil, Nil)
       }
-    }
-    (Nil, Nil)
+
+    val fields = obj.getClass.getDeclaredFields.filter(_.getName == "$outer").toList
+    loop(fields)
   }
 
   /** Return a list of classes that represent closures enclosed in the given closure object.
@@ -89,17 +97,20 @@ object ClosureCleaner {
       if (cr != null) {
         val set = mutable.Set.empty[Class[_]]
         cr.accept(new InnerClosureFinder(set), 0)
-        for (cls <- set -- seen) {
+        for (cls <- set.toSet -- seen) {
           seen += cls
           stack.push(cls)
         }
       }
     }
-    (seen - obj.getClass).toList
+    (seen.toSet - obj.getClass).toList
   }
 
   /** Initializes the accessed fields for outer classes and their super classes. */
-  private def initAccessedFields(accessedFields: mutable.Map[Class[_], mutable.Set[String]], outerClasses: Seq[Class[_]]): Unit = {
+  private def initAccessedFields(
+      accessedFields: mutable.Map[Class[_], mutable.Set[String]],
+      outerClasses: Seq[Class[_]]
+  ): Unit = {
     for (cls <- outerClasses) {
       var currentClass = cls
       assert(currentClass != null, "The outer class can't be null.")
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/ConnectedStreams.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/ConnectedStreams.scala
index 4e49346..561c8c3 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/ConnectedStreams.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/ConnectedStreams.scala
@@ -189,7 +189,7 @@ class ConnectedStreams[IN1, IN2](javaStream: JavaCStream[IN1, IN2]) {
     * @return
     *   The resulting data stream.
     */
-  def flatMap[R: TypeInformation](fun1: IN1 => TraversableOnce[R], fun2: IN2 => TraversableOnce[R]): DataStream[R] = {
+  def flatMap[R: TypeInformation](fun1: IN1 => IterableOnce[R], fun2: IN2 => IterableOnce[R]): DataStream[R] = {
 
     if (fun1 == null || fun2 == null) {
       throw new NullPointerException("FlatMap functions must not be null.")
@@ -198,8 +198,8 @@ class ConnectedStreams[IN1, IN2](javaStream: JavaCStream[IN1, IN2]) {
     val cleanFun2 = clean(fun2)
 
     val flatMapper = new CoFlatMapFunction[IN1, IN2, R] {
-      def flatMap1(value: IN1, out: Collector[R]): Unit = { cleanFun1(value).foreach(out.collect) }
-      def flatMap2(value: IN2, out: Collector[R]): Unit = { cleanFun2(value).foreach(out.collect) }
+      def flatMap1(value: IN1, out: Collector[R]): Unit = { cleanFun1(value).iterator.foreach(out.collect) }
+      def flatMap2(value: IN2, out: Collector[R]): Unit = { cleanFun2(value).iterator.foreach(out.collect) }
     }
 
     flatMap(flatMapper)
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/DataStream.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/DataStream.scala
index 52e3c30..1befbf3 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/DataStream.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/DataStream.scala
@@ -560,13 +560,13 @@ class DataStream[T](stream: JavaStream[T]) {
 
   /** Creates a new DataStream by applying the given function to every element and flattening the results.
     */
-  def flatMap[R: TypeInformation](fun: T => TraversableOnce[R]): DataStream[R] = {
+  def flatMap[R: TypeInformation](fun: T => IterableOnce[R]): DataStream[R] = {
     if (fun == null) {
       throw new NullPointerException("FlatMap function must not be null.")
     }
     val cleanFun = clean(fun)
     val flatMapper = new FlatMapFunction[T, R] {
-      def flatMap(in: T, out: Collector[R]): Unit = { cleanFun(in).foreach(out.collect) }
+      def flatMap(in: T, out: Collector[R]): Unit = { cleanFun(in).iterator.foreach(out.collect) }
     }
     flatMap(flatMapper)
   }
@@ -690,8 +690,10 @@ class DataStream[T](stream: JavaStream[T]) {
     * For cases where the timestamps are not monotonously increasing, use the more general methods
     * [[assignTimestampsAndWatermarks(AssignerWithPeriodicWatermarks)]] and
     * [[assignTimestampsAndWatermarks(AssignerWithPunctuatedWatermarks)]].
+    * 
+    * @deprecated Please use {@link #assignTimestampsAndWatermarks(WatermarkStrategy)} instead.
     */
-  @PublicEvolving
+  @Deprecated
   def assignAscendingTimestamps(extractor: T => Long): DataStream[T] = {
     val cleanExtractor = clean(extractor)
     val extractorFunction = new AscendingTimestampExtractor[T] {
@@ -754,8 +756,12 @@ class DataStream[T](stream: JavaStream[T]) {
   def printToErr(sinkIdentifier: String): DataStreamSink[T] = stream.printToErr(sinkIdentifier)
 
   /** Writes a DataStream using the given [[OutputFormat]].
-    */
-  @PublicEvolving
+   * 
+   * @deprecated Please use the {@link
+   *     org.apache.flink.streaming.api.functions.sink.filesystem.StreamingFileSink} explicitly
+   *     using the {@link #addSink(SinkFunction)} method.
+   */
+  @Deprecated
   def writeUsingOutputFormat(format: OutputFormat[T]): DataStreamSink[T] = {
     stream.writeUsingOutputFormat(format)
   }
@@ -790,7 +796,10 @@ class DataStream[T](stream: JavaStream[T]) {
 
   /** Adds the given sink to this DataStream. Only streams with sinks added will be executed once the
     * StreamExecutionEnvironment.execute(...) method is called.
+    * 
+    * @deprecated Please use the sinkTo(sink: org.apache.flink.api.connector.sink2.Sink[T])
     */
+  @Deprecated  
   def sinkTo(sink: org.apache.flink.api.connector.sink.Sink[T, _, _, _]): DataStreamSink[T] =
     stream.sinkTo(sink)
 
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/KeyedStream.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/KeyedStream.scala
index 2780e66..d5156e2 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/KeyedStream.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/KeyedStream.scala
@@ -460,7 +460,7 @@ class KeyedStream[T, K](javaStream: KeyedJavaStream[T, K]) extends DataStream[T]
     * Note that the user state object needs to be serializable.
     */
   def flatMapWithState[R: TypeInformation, S: TypeInformation](
-      fun: (T, Option[S]) => (TraversableOnce[R], Option[S])
+      fun: (T, Option[S]) => (IterableOnce[R], Option[S])
   ): DataStream[R] = {
     if (fun == null) {
       throw new NullPointerException("Flatmap function must not be null.")
@@ -470,12 +470,12 @@ class KeyedStream[T, K](javaStream: KeyedJavaStream[T, K]) extends DataStream[T]
     val stateTypeInfo: TypeInformation[S] = implicitly[TypeInformation[S]]
     val serializer: TypeSerializer[S]     = stateTypeInfo.createSerializer(javaStream.getExecutionConfig)
 
-    val flatMapper = new RichFlatMapFunction[T, R] with StatefulFunction[T, TraversableOnce[R], S] {
+    val flatMapper = new RichFlatMapFunction[T, R] with StatefulFunction[T, IterableOnce[R], S] {
 
       override val stateSerializer: TypeSerializer[S] = serializer
 
       override def flatMap(in: T, out: Collector[R]): Unit = {
-        applyWithState(in, cleanFun).foreach(out.collect)
+        applyWithState(in, cleanFun).iterator.foreach(out.collect)
       }
     }
 
@@ -488,8 +488,10 @@ class KeyedStream[T, K](javaStream: KeyedJavaStream[T, K]) extends DataStream[T]
     *   Name under which to the publish the queryable state instance
     * @return
     *   Queryable state instance
+    * @deprecated The Queryable State feature is deprecated since Flink 1.18, and will be removed in a
+    *     future Flink major version.
     */
-  @PublicEvolving
+  @Deprecated
   def asQueryableState(queryableStateName: String): QueryableStateStream[K, T] = {
     val stateDescriptor = new ValueStateDescriptor(queryableStateName, dataType.createSerializer(executionConfig))
 
@@ -504,8 +506,11 @@ class KeyedStream[T, K](javaStream: KeyedJavaStream[T, K]) extends DataStream[T]
     *   State descriptor to create state instance from
     * @return
     *   Queryable state instance
+    * 
+    * @deprecated The Queryable State feature is deprecated since Flink 1.18, and will be removed in a
+    *     future Flink major version.
     */
-  @PublicEvolving
+  @Deprecated
   def asQueryableState(
       queryableStateName: String,
       stateDescriptor: ValueStateDescriptor[T]
@@ -529,8 +534,10 @@ class KeyedStream[T, K](javaStream: KeyedJavaStream[T, K]) extends DataStream[T]
     *   State descriptor to create state instance from
     * @return
     *   Queryable state instance
+    * @deprecated The Queryable State feature is deprecated since Flink 1.18, and will be removed in a
+    *     future Flink major version.
     */
-  @PublicEvolving
+  @Deprecated
   def asQueryableState(
       queryableStateName: String,
       stateDescriptor: ReducingStateDescriptor[T]
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/StreamExecutionEnvironment.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/StreamExecutionEnvironment.scala
index 2f65196..004fdc0 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/StreamExecutionEnvironment.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/StreamExecutionEnvironment.scala
@@ -487,19 +487,29 @@ class StreamExecutionEnvironment(javaEnv: JavaEnv) {
 
   /** Creates a DataStream that represents the Strings produced by reading the given file line wise. The file will be
     * read with the system's default character set.
+    * 
+    * @deprecated Use {@code
+    *     FileSource#forRecordStreamFormat()/forBulkFileFormat()/forRecordFileFormat() instead}.
     */
+  @Deprecated  
   def readTextFile(filePath: String): DataStream[String] =
     asScalaStream(javaEnv.readTextFile(filePath))
 
   /** Creates a data stream that represents the Strings produced by reading the given file line wise. The character set
     * with the given name will be used to read the files.
+    * @deprecated Use {@code
+    *     FileSource#forRecordStreamFormat()/forBulkFileFormat()/forRecordFileFormat() instead}.
     */
+  @Deprecated  
   def readTextFile(filePath: String, charsetName: String): DataStream[String] =
     asScalaStream(javaEnv.readTextFile(filePath, charsetName))
 
   /** Reads the given file with the given input format. The file path should be passed as a URI (e.g.,
     * "file:///some/local/file" or "hdfs://host:port/file/path").
+    * @deprecated Use {@code
+    *     FileSource#forRecordStreamFormat()/forBulkFileFormat()/forRecordFileFormat() instead}.
     */
+  @Deprecated  
   def readFile[T: TypeInformation](inputFormat: FileInputFormat[T], filePath: String): DataStream[T] =
     asScalaStream(javaEnv.readFile(inputFormat, filePath))
 
@@ -526,8 +536,11 @@ class StreamExecutionEnvironment(javaEnv: JavaEnv) {
     *   In the case of periodic path monitoring, this specifies the interval (in millis) between consecutive path scans
     * @return
     *   The data stream that represents the data read from the given file
+    * 
+    * @deprecated Use {@code
+    *     FileSource#forRecordStreamFormat()/forBulkFileFormat()/forRecordFileFormat() instead}.
     */
-  @PublicEvolving
+  @Deprecated
   def readFile[T: TypeInformation](
       inputFormat: FileInputFormat[T],
       filePath: String,
@@ -563,7 +576,13 @@ class StreamExecutionEnvironment(javaEnv: JavaEnv) {
     * have a parallelism of 1. To enable parallel execution, the user defined source should implement
     * ParallelSourceFunction or extend RichParallelSourceFunction. In these cases the resulting source will have the
     * parallelism of the environment. To change this afterwards call DataStreamSource.setParallelism(int)
+    * 
+    * @deprecated This method relies on the {@link
+    *     org.apache.flink.streaming.api.functions.source.SourceFunction} API, which is due to be
+    *     removed. Use the {@link #fromSource[TypeInformation](Source, WatermarkStrategy, String)}
+    *     method based on the new {@link org.apache.flink.api.connector.source.Source} API instead.
     */
+  @Deprecated
   def addSource[T: TypeInformation](function: SourceFunction[T]): DataStream[T] = {
     require(function != null, "Function must not be null.")
 
@@ -573,7 +592,13 @@ class StreamExecutionEnvironment(javaEnv: JavaEnv) {
   }
 
   /** Create a DataStream using a user defined source function for arbitrary source functionality.
-    */
+   * 
+   * @deprecated This method relies on the {@link
+   *     org.apache.flink.streaming.api.functions.source.SourceFunction} API, which is due to be
+   *     removed. Use the {@link #fromSource[TypeInformation](Source, WatermarkStrategy, String)}
+   *     method based on the new {@link org.apache.flink.api.connector.source.Source} API instead.
+   */
+  @Deprecated
   def addSource[T: TypeInformation](function: SourceContext[T] => Unit): DataStream[T] = {
     require(function != null, "Function must not be null.")
     val sourceFunction = new SourceFunction[T] {
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnConnectedStream.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnConnectedStream.scala
index db47206..011d558 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnConnectedStream.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnConnectedStream.scala
@@ -63,8 +63,8 @@ class OnConnectedStream[IN1, IN2](stream: ConnectedStreams[IN1, IN2]) {
     */
   @PublicEvolving
   def flatMapWith[R: TypeInformation](
-      flatMap1: IN1 => TraversableOnce[R],
-      flatMap2: IN2 => TraversableOnce[R]
+      flatMap1: IN1 => IterableOnce[R],
+      flatMap2: IN2 => IterableOnce[R]
   ): DataStream[R] =
     stream.flatMap(flatMap1, flatMap2)
 
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnDataStream.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnDataStream.scala
index 9856f06..2f5ccda 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnDataStream.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/extensions/impl/acceptPartialFunctions/OnDataStream.scala
@@ -55,7 +55,7 @@ class OnDataStream[T](stream: DataStream[T]) {
     *   A dataset of R
     */
   @PublicEvolving
-  def flatMapWith[R: TypeInformation](fun: T => TraversableOnce[R]): DataStream[R] =
+  def flatMapWith[R: TypeInformation](fun: T => IterableOnce[R]): DataStream[R] =
     stream.flatMap(fun)
 
   /** Applies a predicate `fun` to each item of the stream, keeping only those for which the predicate holds
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaAllWindowFunction.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaAllWindowFunction.scala
index 1ffe571..43b1500 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaAllWindowFunction.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaAllWindowFunction.scala
@@ -22,7 +22,7 @@ import org.apache.flink.streaming.api.functions.windowing.{AllWindowFunction =>
 import org.apache.flink.streaming.api.windowing.windows.Window
 import org.apache.flink.util.Collector
 
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 /** A wrapper function that exposes a Scala Function3 as a Java AllWindowFunction.
   */
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaProcessWindowFunctionWrapper.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaProcessWindowFunctionWrapper.scala
index ba3db6e..68f1dfa 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaProcessWindowFunctionWrapper.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaProcessWindowFunctionWrapper.scala
@@ -29,7 +29,7 @@ import org.apache.flink.streaming.api.functions.windowing.{
 import org.apache.flink.streaming.api.windowing.windows.Window
 import org.apache.flink.util.Collector
 
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 /** A wrapper function that exposes a Scala ProcessWindowFunction as a ProcessWindowFunction function.
   *
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaWindowFunction.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaWindowFunction.scala
index 45ea814..9d68ca0 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaWindowFunction.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/function/util/ScalaWindowFunction.scala
@@ -22,7 +22,7 @@ import org.apache.flink.streaming.api.functions.windowing.{WindowFunction => JWi
 import org.apache.flink.streaming.api.windowing.windows.Window
 import org.apache.flink.util.Collector
 
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 /** A wrapper function that exposes a Scala Function4 as a Java WindowFunction.
   */
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/CaseClassTypeInfo.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/CaseClassTypeInfo.scala
index bf1b556..637076d 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/CaseClassTypeInfo.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/CaseClassTypeInfo.scala
@@ -34,7 +34,7 @@ import Keys.ExpressionKeys
 import org.apache.flink.api.java.typeutils.TupleTypeInfoBase
 
 import scala.annotation.{nowarn, tailrec}
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 import scala.collection.mutable.ArrayBuffer
 
 /** TypeInformation for Case Classes. Creation and access is different from our Java Tuples so we have to treat them
@@ -198,27 +198,32 @@ abstract class CaseClassTypeInfo[T <: Product](
       field = "_" + (Integer.valueOf(field) + 1)
     }
 
-    for (i <- fieldNames.indices) {
-      if (fieldNames(i) == field) {
-        if (tail == null) {
-          return getTypeAt(i)
-        } else {
-          fieldTypes(i) match {
-            case co: CompositeType[_] =>
-              return co.getTypeAt(tail)
-            case _ =>
-              throw new InvalidFieldReferenceException(
-                "Nested field expression \"" + tail +
-                  "\" not possible on atomic type " + fieldTypes(i) + "."
-              )
-          }
-        }
+    @tailrec
+    def loop(indices: List[Int]): TypeInformation[X] =
+      indices match {
+        case i :: ii =>
+          if (fieldNames(i) == field) {
+            if (tail == null) {
+              getTypeAt(i)
+            } else {
+              fieldTypes(i) match {
+                case co: CompositeType[_] =>
+                  co.getTypeAt(tail)
+                case _ =>
+                  throw new InvalidFieldReferenceException(
+                    "Nested field expression \"" + tail +
+                      "\" not possible on atomic type " + fieldTypes(i) + "."
+                  )
+              }
+            }
+          } else loop(ii)
+        case Nil =>
+          throw new InvalidFieldReferenceException(
+            s"Unable to find field \"$field\" in type $this."
+          )
       }
-    }
-    throw new InvalidFieldReferenceException(
-      "Unable to find field \"" + field +
-        "\" in type " + this + "."
-    )
+
+    loop(fieldNames.indices.toList)
   }
 
   @PublicEvolving
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/EitherTypeInfo.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/EitherTypeInfo.scala
index 8044310..1ec843f 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/EitherTypeInfo.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/EitherTypeInfo.scala
@@ -24,7 +24,7 @@ import org.apache.flink.api.common.typeinfo.TypeInformation
 import org.apache.flink.api.common.typeutils.TypeSerializer
 
 import scala.annotation.nowarn
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 /** TypeInformation [[Either]].
   */
diff --git a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/OptionTypeInfo.scala b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/OptionTypeInfo.scala
index 29a9dec..da37c0d 100644
--- a/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/OptionTypeInfo.scala
+++ b/modules/scala-api/src/main/scala/org/apache/flinkx/api/typeinfo/OptionTypeInfo.scala
@@ -24,7 +24,7 @@ import org.apache.flink.api.common.typeinfo.{AtomicType, TypeInformation}
 import org.apache.flink.api.common.typeutils.{TypeComparator, TypeSerializer}
 
 import scala.annotation.nowarn
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 /** TypeInformation for [[Option]].
   */