Don't sign it unless you mean it. I wouldn't. If that clause is enforceable (which varies by state), the copyright to your code is assigned to your employer as

Don't sign it unless you mean it. I wouldn't. If that clause is enforceable (which varies by state), the copyright to your code is assigned to your employer as soon as you write it, so you have no right to contribute it to the GPL project. If you don't have that right but contribute anyway, the project would be infringing on your employer's copyrights. Not a great situation to put them in. IANAL