I came across the same issue, but one could argue that camel case by definition starts with a lower case letter.
I suggest to improve the description to be more precice about the imput the method receives.

Something like:
"Only valid camelCase strings will be passed into the method. No PascalCase or sentence are passed"

Otherwise a sentence like "PascalCase is not camelCase, says Chris" would also lead to incorrect results. IMHO.