Java to Kotlin converter: even more smartness about nullability

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

@@ -0,0 +1,9 @@
+class C() {
+    private var s: String? = ""
+
+    fun foo() {
+        if (s == null) {
+            System.out.print("null")
+        }
+    }
+}