Java to Kotlin converter: and even more smartness about nullability

#KT-5162 Fixed

j2k/tests/testData/ast/nullability/MethodResultComparedWithNull.java

@@ -0,0 +1,12 @@
+//file
+interface I {
+    String getString();
+}
+
+class C {
+    void foo(I i) {
+        if (i.getString() == null) {
+            println("null")
+        }
+    }
+}