Java to Kotlin converter: and even more smartness about nullability

#KT-5162 Fixed

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

@@ -0,0 +1,8 @@
+class C() {
+    private fun foo(s: String?) {
+    }
+
+    fun bar() {
+        foo(null)
+    }
+}