Java to Kotlin converter: even more smartness about nullability

j2k/tests/testData/ast/nullability/FieldComparedWithNull4.kt

@@ -0,0 +1,7 @@
+class C(private var s: String?) {
+    {
+        if (s == null) {
+            System.out.print("null")
+        }
+    }
+}