If you delete all the numbers from a field in the RGB section of colour calculator in the Context Free GUI you get the following message pop up:
There are buttons to Continue, Quit or show more details.Unhandled exception has occurred in your application. If you click Continue, the application will ignore this error and attempt to continue. If you click Quit the application will close immediately.
Input string was not in a correct format.
Severity:
Possible data loss. I was a bit worried when the message popped up and had thought the program had crashed and I would lose my work. Would be easy enough to skim the message and click quit.
How to reproduce:
Open the colour calculator and delete all the text in one of the RGB fields.
Version:
Context Free 3.0.5 (v34) 64-Bit on Windows 8.1
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Hope this helps!