I recently compiled php 4.2.3 on my debian system under apache 2.0. I then uploaded a site that was developed on another machine running apache 1.3 and php 4.2.1. While testing the site i noticed something seemed wrong. Upon further investigation i found that the is_null function, which was working perfectly on the other system, seemed to be malfunctioning.

for example:
if (is_null($somevar)){
   execute code A
}

code A would execute regardless of whether $somevar had a null value or not

if i do the following:
echo is_null($somevar) 
nothing was echoed to the screen, again regardless of the value of $somevar

if i did the following however with $somevar set to null:
if($somevar == null){
   execute code A
   if(is_null($somevar)){
      execute code b
   }
}

code A will execute but code B will not. 

the value of somevar is assigned by an html form sent using the POST method as this example illustrates:

$somevar = $_POST['$formvar'];

the purpose of the code is to check if a field was left blank.
This code worked fine on the original server but failed to work when copied to the new server

my configuration is as follows:
./configure' '--prefix=/usr/local/apache2/php' '--with-apxs2=/usr/local/apache2/bin/apxs' '--with-config-file-path=/etc' '--with-mysql'