Do not suggest adding !! on null constant #KT-14643 Fixed

idea/testData/quickfix/addExclExclCall/null.kt

@@ -0,0 +1,8 @@
+// "Add non-null asserted (!!) call" "false"
+// ACTION: Add 'const' modifier
+// ACTION: Add 'toString()' call
+// ACTION: Change type of 'x' to 'String?'
+// ACTION: Convert property initializer to getter
+// ERROR: Null can not be a value of a non-null type String
+
+val x: String = null<caret>