Several classes in PHP return null when there is a problem in the
parameters passed to their constructor e.g.
[...]
Several constructors check the parameters that they are given.....and
then just give a warning when they are not acceptable. e.g.
[...]
Some constructors check the parameters they are given, and then emit
either a 'Catchable fatal error' error or other error e.g.
Classes implemented in C / provided by PHP must not have any of
the above issues. +1 for fixing them.