Java to Kotlin converter: even more smartness about nullability

j2k/tests/testData/ast/nullability/FieldComparedWithNull2.java

@@ -0,0 +1,14 @@
+//file
+class C {
+    private String s;
+
+    public C(String s) {
+        this.s = s;
+    }
+
+    void foo() {
+        if (s != null) {
+            System.out.print("not null");
+        }
+    }
+}