private static String getAttributeValue(PsiAnnotation annotation, String attribute) {
    PsiAnnotationMemberValue value = annotation.findAttributeValue(attribute);
    if (value == null) {
      return null;
    }
    if (value instanceof PsiExpression) {
      Object res = ExpressionUtils.computeConstantExpression(((PsiExpression)value));
      if (res instanceof String) {
        return (String)res;
      }
    }
    throw new IllegalStateException("Constant string expression expected, but was " + value);
  }
private static String getAttributeValue(PsiAnnotation annotation, String attribute)