Test whether the structure is empty. The default implementation is
Left-associative and lazy in both the initial element and the
accumulator. Thus optimised for structures where the first element can
be accessed in constant time. Structures where this is not the case
should have a non-default implementation.
Examples
Basic usage:
>>> null []
True
>>> null [1]
False
null is expected to terminate even for infinite structures. The
default implementation terminates provided the structure is bounded on
the left (there is a leftmost element).
>>> null [1..]
False