fix search condition (#1279)

* fix search condition

partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/PlanTyper.kt

@@ -646,9 +646,15 @@ internal class PlanTyper(
             }
         }
 
+        /**
+         * In this context, Boolean means PartiQLValueType Bool, which can be nullable.
+         * Hence, we permit Static Type BOOL, Static Type NULL, Static Type Missing here.
+         */
         private fun canBeBoolean(type: StaticType): Boolean {
             return type.flatten().allTypes.any {
-                it is BoolType
+                // TODO: This is a quick fix to unblock the typing or case expression.
+                //  We need to model the truth value better in typer.
+                it is BoolType || it is NullType || it is MissingType
             }
         }
 

partiql-planner/src/test/kotlin/org/partiql/planner/internal/typer/functions/NullIfTest.kt

@@ -0,0 +1,35 @@
+package org.partiql.planner.internal.typer.functions
+
+import org.junit.jupiter.api.DynamicContainer
+import org.junit.jupiter.api.TestFactory
+import org.partiql.planner.internal.typer.PartiQLTyperTestBase
+import org.partiql.planner.util.allSupportedType
+import org.partiql.planner.util.cartesianProduct
+import org.partiql.types.StaticType
+import java.util.stream.Stream
+
+// TODO: Model handling of Truth Value in typer better.
+class NullIfTest : PartiQLTyperTestBase() {
+
+    @TestFactory
+    fun nullIf(): Stream<DynamicContainer> {
+        val tests = listOf(
+            "func-00",
+        ).map { inputs.get("basics", it)!! }
+
+        val argsMap = buildMap {
+            val successArgs = cartesianProduct(allSupportedType, allSupportedType)
+
+            successArgs.forEach { args: List<StaticType> ->
+                val returnType = StaticType.unionOf(args.first(), StaticType.NULL).flatten()
+                (this[TestResult.Success(returnType)] ?: setOf(args)).let {
+                    put(TestResult.Success(returnType), it + setOf(args))
+                }
+                Unit
+            }
+            put(TestResult.Failure, emptySet<List<StaticType>>())
+        }
+
+        return super.testGen("nullIf", tests, argsMap)
+    }
+}

partiql-planner/src/testFixtures/resources/inputs/basics/functions.sql

@@ -0,0 +1,2 @@
+--#[func-00]
+nullIf(t1, t2);