How to only use namespace if it exists?

Hi there, I'm trying to make an asset. This is a script I want to make compatible for both TextMeshPro users, and people who don't use TextMeshPro. To use TextMeshPro variables (for example: private TextMeshPro textMeshPro), you need to include: **using TMPro;** This however throws an error when the TextMeshPro asset *is not being used*.
So the thing is that I only need to use this namespace if the TextMeshPro asset is installed. I can't use custom defines, because then I won't be able to share this when it's finished.
Is there anyway I can prevent this error?