bool = cpattern:IsNull()
True if the pattern is NULL, i.e. invalid. If functions
that allocate patterns fail, they might not throw an error but simply set the
pattern to NULL. You can use this function to check if pattern allocation has
failed in which case the pattern will be NULL.
Also, certain getter functions can return a NULL object in case the object
doesn't exist. You can use this function to check if a getter function returned
a NULL handle.
True if the pattern is NULL, otherwise False