Default generic type arguments when resolving KType from a Class.

We now fill up missing KTypeProjection arguments with star because the Kotlin Reflection.typeOf resolution fails if arguments are not provided.

Closes #3041
Original pull request: #3048

src/main/java/org/springframework/data/mapping/model/KotlinValueUtils.java

@@ -25,10 +25,12 @@ import kotlin.reflect.KParameter;
 import kotlin.reflect.KProperty;
 import kotlin.reflect.KType;
 import kotlin.reflect.KTypeParameter;
+import kotlin.reflect.KTypeProjection;
 import kotlin.reflect.jvm.ReflectJvmMapping;
 
 import java.lang.reflect.Type;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -39,6 +41,7 @@ import org.springframework.util.Assert;
  * Utilities for Kotlin Value class support.
  *
  * @author Mark Paluch
+ * @author Christoph Strobl
  * @since 3.2
  */
 class KotlinValueUtils {
@@ -72,7 +75,28 @@ class KotlinValueUtils {
 	public static ValueBoxing getConstructorValueHierarchy(Class<?> cls) {
 
 		KClass<?> kotlinClass = JvmClassMappingKt.getKotlinClass(cls);
-		return new ValueBoxing(BoxingRules.CONSTRUCTOR, Reflection.typeOf(kotlinClass), kotlinClass, false);
+		KType kType = extractKType(kotlinClass);
+		return new ValueBoxing(BoxingRules.CONSTRUCTOR, kType, kotlinClass, false);
+	}
+
+	/**
+	 * Get the {@link KType} for a given {@link KClass} and potentially fill missing generic type arguments with
+	 * {@link KTypeProjection#star} to prevent Kotlin internal checks to fail.
+	 *
+	 * @param kotlinClass
+	 * @return
+	 */
+	private static KType extractKType(KClass<?> kotlinClass) {
+
+		return kotlinClass.getTypeParameters().isEmpty() ? Reflection.typeOf(kotlinClass)
+				: Reflection.typeOf(JvmClassMappingKt.getJavaClass(kotlinClass), stubKTypeProjections(kotlinClass));
+	}
+
+	private static KTypeProjection[] stubKTypeProjections(KClass<?> kotlinClass) {
+
+		KTypeProjection[] kTypeProjections = new KTypeProjection[kotlinClass.getTypeParameters().size()];
+		Arrays.fill(kTypeProjections, KTypeProjection.star);
+		return kTypeProjections;
 	}
 
 	/**