In section 3.5.3 Shell Parameter Expansion: In the sixth paragraph it correctly states that "Bash tests for a parameter that is unset *or* null" when you use the colon. It later attempts to restate this but fails by saying "if the colon is included, the operator tests for both parameter's existence *and* that its value is not null"
This caused me quite some consternation, but only for about a minute. Not an emergency to fix, but would be best if it was fixed at some point, especially since it should be easy. Hope I helped! -mcmuffin6o
