令人困惑的SalesForce错误

I'm using the SalesForce PHP Toolkit and getting a connection just fine. But when I use any of the example code - see here

INVALID_FIELD: No such column '' on entity 'Contact'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.

I might just be struggling to find the answer because Google won't let me search for ''

The environment is CentOS 6 with PHP 5.3.

I just created an account here to answer this question. It took me all day long to find out this bug in PHP Toolkit. The problem is caused by the "fieldsToNull" property. I read an approx. solution here that gave me an idea where to look for the solution.

So a correct example would be:

 $fields = array('LastName' => 'Doe');
 $sObject = new SObject();
 $sObject->fields = $fields;
 $sObject->fieldsToNull = NULL;//this is the solution! :)      
 $sObject->type = 'Contact';

Then, proceed as usual with the remaining part of the examples of the PHP Toolkit. It worked fine with my Partner WSDL+Developer SF Account.

Hope it helps!