For the c++ api dox this expands to "\c nullptr" (the
\c directive indicates a code literal value), and for sipify/Python
it expands to ``None`` (`` is sphinx annotation for literal values)
Makes for nicer dox for both c++ and Python!
bool(obj) in Python has the following semantics:
1. if the object has __bool__() method, return its value
2. if the object has __len__() method, return its value
3. return True
So for objects in QGIS API that implement __len__() method, we were getting
unexpected behavior - for example, "if layer: ..." would evaluate as False
in case the layer was empty, while the usual expectation is that any reference
to an object that is not None should evaluate to True.
Checks whether a function declaration has parameters that are
top level const.
const values in declarations do not affect the signature of a
function, so they should not be put there.
