Don't change the code in the collections module.  While semantically valid, the change obfuscates the code.  The meaning of maxlen < 0 is that there is no maximum length.  I don't want this test hidden; otherwise, I would have changed it long ago as was done elsewhere in the module where it made sense.

Elsewhere, consider making a macro with clear name and comment (as was done with NEEDS_TRIM) in the collections module.  Otherwise, you're just leaving behind constipated and tricky code with no indication of why a signed variable is being coerced to unsigned.