public PsiElement doIntroduceParameter(PsiElement expression, PyAssignmentStatement declaration) {
    PyFunction function = PsiTreeUtil.getParentOfType(expression, PyFunction.class);
    if (function != null && declaration != null) {
      PyParameterList parameterList = function.getParameterList();
      parameterList.addParameter(PyElementGenerator.getInstance(function.getProject()).createParameter(declaration.getText()));
      CodeInsightUtilCore.forcePsiPostprocessAndRestoreElement(function);
      return parameterList.findParameterByName(declaration.getTargets()[0].getText());
    }
    return null;
  }
public PsiElement doIntroduceParameter(PsiElement expression, PyAssignmentStatement declaration)