I have a combo box with the following configuration. The valid values that can be submitted are integers and the empty string. When I submit the form I would like to be able to leave these combo box empty, that is I don't want the user to have to select a value. In firefox when I submit the form with the empty combobox the posted value goes to the server as and empty string and the server handles the request parameter properly. In IE the value is submitted as the string 'null'. This causes a problem because the application is not expecting a populated string in the request parameter. I would like to be able to deal with this on the client side rather than the server if possible. Any suggestions?

triggerAction: 'all',
mode: 'local',
valueField: valueField,
displayField: displayField,
name: config.name,
hiddenName: config.name,
hiddenId: config.name + '_id',
forceSelection: false,
typeAhead: true,
validateOnBlur: false,
hiddenValue: '',