Questions asking for code to be written to solve a specific problem are off-topic here as there is no code to review.
However, some of these questions actually have some code in them already, so the wording "there is no code to review" isn't totally correct. Sometimes they are asking for more code to be written. But the code that they actually have in the question works, so this other close reason is not a better option:
Your question must contain working code for us to review it here. For questions regarding specific problems encountered while coding, try Stack Overflow. After getting your code to work, you may edit this question seeking a review of your working code.
The way I see it, our "Questions asking for code to be written" is our corresponding reason to StackOverflow's
Questions asking for code must demonstrate a minimal understanding of the problem being solved. Include attempted solutions, why they didn't work, and the expected results. See also: Stack Overflow question checklist
Which is a good reason for not including a link to Stack Overflow in the text. If we would link to Stack Overflow, it would very likely be asked there and then closed on Stack Overflow too.
However, what I think we should do is to change "Questions asking for code to be written to solve a specific problem are off-topic here as there is no code to review." to something that includes the possibility that there might be some code already.
What I propose is: (Changes in italics)
Questions asking for code to be written to solve a specific problem are off-topic here as there is no code to review, or the current code is not yet ready for a review."
If you have other proposal for how to change the wording, feel free to add an answer.
If you think the wording does not need to be changed at all, feel free to downvote me into oblivion.