J2K: enum constants are non-nullable

j2k/tests/testData/ast/enum/class/enumConstantIsNotNull.jav

@@ -0,0 +1,7 @@
+enum E {
+  FOO;
+
+  void foo() {
+    FOO.toString();
+  }
+}

j2k/tests/testData/ast/enum/class/enumConstantIsNotNull.kt

@@ -0,0 +1,8 @@
+enum class E {
+FOO
+fun foo() : Unit {
+FOO.toString()
+}
+public fun name() : String { return "" }
+public fun order() : Int { return 0 }
+}