Change decorative image from error to warning

What is the markup being output? If all is working correctly:

• no alt attribute: error, missing alt. Screen reader behavior varies, but generally speaks filename or file url.
• alt="" (empty quotes): warning/manual check for decorative image. Screen reader ignores image.
• alt="""" (quotes containing quotes): error, because this is not marked decorative, but rather is technically valid alt text made of quote characters. Screen reader announces that there is an image, but just makes an awkward silence when it reads the alt as it iterates through characters it does not pronounce.

I'm closing this for now as it is working as designed; please re-open if I have misinterpreted.