Revert "Upgrade to Kotlin 1.4 M2"

This reverts commit 2a74eff10f.

Some regressions require to wait at least Kotlin 1.4 M3.

spring-messaging/spring-messaging.gradle

@@ -2,12 +2,6 @@ description = "Spring Messaging"
 
 apply plugin: "kotlin"
 
-// Workaround for https://youtrack.jetbrains.com/issue/KT-39610
-configurations["optional"].attributes.attribute(
-		org.gradle.api.attributes.Usage.USAGE_ATTRIBUTE,
-		objects.named(Usage.class, "java-runtime")
-)
-
 dependencies {
 	compile(project(":spring-beans"))
 	compile(project(":spring-core"))

spring-messaging/src/test/kotlin/org/springframework/messaging/simp/annotation/support/SimpAnnotationMethodMessageHandlerKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020  the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -132,7 +132,7 @@ class SimpAnnotationMethodMessageHandlerKotlinTests {
         messageHandler.registerHandler(testController)
         messageHandler.handleMessage(message)
         assertThat(testController.exception).isNotNull()
-		assertThat(testController.exception).isInstanceOf(NullPointerException::class.java)
+		assertThat(testController.exception).isInstanceOf(IllegalArgumentException::class.java)
     }
 
     private fun createMessage(destination: String, headers: Map<String, String?>): Message<ByteArray> {