better condition logic now properly handles correctly these cases:

  extra_attributes:
    type: object
    additionalProperties: true

  extra_attributes:
    type: object
    additionalProperties: {}

  extra_attributes:
    additionalProperties: true

but fails for this case, which might not be an issue (or an issue with zio-schema):

  extra_attributes:
    additionalProperties: {}

zio-http/shared/src/main/scala/zio/http/endpoint/openapi/JsonSchema.scala

@@ -255,14 +255,29 @@ object JsonSchema {
 
   private[openapi] def fromSerializableSchema(schema: SerializableJsonSchema): JsonSchema = {
 
+    val definedAttributesCount = schema.productIterator.count(_.asInstanceOf[Option[_]].isDefined)
+
     // if type: object with additionalProperties defined,
     // but nothing else, we should assume a free form object
-    def anyObject: Boolean = schema.additionalProperties.collect { case BoolOrSchema.BooleanWrapper(true) =>
-      schema.schemaType.contains(TypeOrTypes.Type("object")) &&
-      schema.productIterator.count(_.asInstanceOf[Option[_]].isDefined) == 2
-    }.exists(identity)
+    // if type is not defined, but additionalProperties is,
+    // and nothing else, object is assumed again.
+    // if both type: object and additionalProperties are defined,
+    // and nothing else, object is assumed.
+    def anyObject: Boolean = {
+      val isObject = schema.schemaType.contains(TypeOrTypes.Type("object"))
+      val hasAttrs = schema.additionalProperties.collect { case BoolOrSchema.BooleanWrapper(b) =>
+        b
+      }.exists(identity)
+
+      // if definedAttributesCount == 0, this also yields true,
+      // but we check for it before calling this function,
+      // thus no need to check it here.
+      val isAnyObj = List(isObject, hasAttrs).count(identity) == definedAttributesCount
+
+      isAnyObj
+    }
 
-    if (schema.productIterator.forall(_.asInstanceOf[Option[_]].isEmpty)) JsonSchema.AnyJson
+    if (definedAttributesCount == 0) JsonSchema.AnyJson
     else if (anyObject) JsonSchema.Object(Map.empty, Right(JsonSchema.AnyJson), Chunk.empty)
     else {
       val additionalProperties = schema.additionalProperties match {