Received this error message when saving

Something weird happens when I save a file. The file says it saves successfully but then an error appears that states the following;

a red box appears and states

write file failed: Cannot read properties of null (reading ‘indexOf’)

this happens when saving any file.

I am sure it is a simple fix

Does this happen with specific documents or is it more random?

I have come to find that this error happens when there is an error of origin when copying CSS or HTML from one document to another. What I mean is I have CSS documents that I use as templates and I found when I copied certain files into a Wappler css main file sometimes that error would occur. I would just debug the document and found that once I repaired a linked file or a WebKit import that error would disappear.