jQuery.event.add() does not check against undefined handlers

[hyponiq]

This is a cross browser issue:

jQuery.event.add() does not check whether 'handler' has been defined. An error is thrown (in (at least) all major browser) when properties of 'handler' are attempted be accessed on an undefined object.

[hyponiq]

I have, in my own copy of jQuery, fixed the issue (for brevity, irrelevant material replaced with "// ... rest ... //"):

jQuery.event = {
	// Bind an event to an element
	// Original by Dean Edwards
	add: function( elem, types, handler, data ) {
                // ... rest ... //
                
		// bug found where on certain occasions, 'hander' is undefined
		if ( handler === undefined ) {
			return;
		}
                
                // ... rest ... //
	},
        
        // ... rest ... //
};

[dmethvin]

Can you provide a test case?

[Rick Waldron]

Duplicate of #7229.