New J2K: Fix existing test data

j2k/testData/fileOrElement/mutableCollections/FunctionReturnValue.new.kt

@@ -1,11 +1,11 @@
-import java.util.ArrayList  
+import java.util.*
 
 internal class A {
-    fun createCollection(): MutableCollection<String?> {
+    fun createCollection(): MutableCollection<String> {
         return ArrayList()
     }
 
-    fun foo(): Collection<String?> {
+    fun foo(): Collection<String> {
         val collection = createCollection()
         collection.add("a")
         return collection

j2k/testData/fileOrElement/mutableCollections/FunctionReturnValue2.new.kt

@@ -1,21 +1,21 @@
-import java.util.ArrayList
+import java.util.*
 
 internal class A {
-    private val collection: MutableCollection<String?>?
+    private val collection: MutableCollection<String>
 
     init {
         collection = createCollection()
     }
 
-    fun createCollection(): MutableCollection<String?> {
+    fun createCollection(): MutableCollection<String> {
         return ArrayList()
     }
 
     fun foo() {
-        collection!!.add("1")
+        collection.add("1")
     }
 
-    fun getCollection(): Collection<String?>? {
+    fun getCollection(): Collection<String> {
         return collection
     }
 }

j2k/testData/fileOrElement/mutableCollections/Iterator2.new.kt

@@ -1,5 +1,5 @@
 class TestMutableCollection {
-    val list: MutableList<String?> = ArrayList()
+    val list: MutableList<String> = ArrayList()
 
     fun test() {
         val it = list.iterator()