public ASTNode createComma() {
    final PsiFile dummyFile = createDummyFile(LanguageLevel.getDefault(), "[0,]");
    final PyAstExpressionStatement expressionStatement = (PyAstExpressionStatement)dummyFile.getFirstChild();
    ASTNode zero = expressionStatement.getFirstChild().getNode().getFirstChildNode().getTreeNext();
    return zero.getTreeNext().copyElement();
  }
public ASTNode createComma()