Converter tests:

Change test data files extension to "java"

j2k/tests/testData/ast/annotations/jetbrainsNotNullChainExpr.java

@@ -0,0 +1,23 @@
+//file
+package test;
+
+import org.jetbrains.annotations.NotNull;
+
+class Foo {
+   void execute() {}
+}
+
+class Bar {
+  @NotNull
+  Foo fooNotNull = Foo();
+  Foo fooNullable = null;
+}
+
+class Test {
+  public void test(@NotNull Bar barNotNull, Bar barNullable) {
+    barNotNull.fooNotNull.execute();
+    barNotNull.fooNullable.execute();
+    barNullable.fooNotNull.execute();
+    barNullable.fooNullable.execute();
+  }
+}