Remove $form = NULL from the code

I had problems with nodefamily.module. After a long debug, I discovered the module uses lines like

That line is present in nodefamily_nodeapi(), where is absolutely useless (it changes the value of $form, which is a local variable, and not a parameter passed by reference to the function).
It is also present in nodefamily_form_alter(), where it has the effect of unsetting all the array keys for the array passed by reference to the function; in that way, all the modules which are trying to change the same form stop to work, and so do the Drupal core modules, which don't find the array keys they set for that kind of form.