private static PsiType getIntFunctionParameterType(PsiExpression argument) {
      PsiType argumentType = FunctionalExpressionUtils.getFunctionalExpressionType(argument);
      return PsiUtil.substituteTypeParameter(argumentType, "java.util.function.IntFunction", 0, false);
    }
private static PsiType getIntFunctionParameterType(PsiExpression argument)