[Form] DataTransformerInterface::transform() api documentation bug

[cordoval]

transferring this ticket symfony/symfony#6539

since i think is best handled this way

forgive and edit this if duplicate or not clear when you label it cc/ @wouterj

[wouterj]

API documentation should be fixed on the symfony/symfony repo by editing the PHPdoc blocks. ( @cordoval )

However, we have documentation about DataTransformers: http://symfony.com/doc/current/cookbook/form/data_transformers.html In that example you can see that we return a string when null is passed, this is correct as the transformers transforms it into a string.

Todo

Just below that example, a note should be placed telling people that you should not always return a string. Something like:

.. note::

    When ``null`` is passed to the ``transform`` method, it should return the
    equivalent value in the correct type. For instance, when it returns strings
    an empty string should be returned and when returning numbers, 0 should
    be returned.

[weaverryan]

Thanks everyone! The note has been added :).