Re: Make foo=null a warning by default.

Hello David,

All is nearly well, although "make docs" found a typo. I should have 
tested doc building before, sorry for this new round which should have 
been avoided.

   "<replacable>null_expression</replaceable>"

s/<replacable>/<replaceable>/;

Also, while reading the full documentation about the setting: I find this 
sentence a bit strange:

"""
But new users are frequently confused about the semantics of expressions 
involving null values, so this option is off by default.
"""

It appears to justify why the option is off by default, but this is not 
the actual reason, which was already provided at the end of the preceding 
paragraph.

I would suggest to remove this "But..." sentence, or turn it differently, 
maybe something like:

""" New users are frequently confused about the semantics of expressions 
involving null values: beware that turning this option on might bring even 
more confusion. """

-- 
Fabien.