In normal mode it returns the value with protected regexp characters.
In regular expression mode it returns the raw value except if the regexp is invalid.
@return {String} The value to process or null if the textfield value is blank or invalid.
@private
function() {
        var me = this,
            value = me.textField.getValue();
            
        if (value === '') {
            return null;
        }
        if (!me.regExpMode) {
            value = value.replace(me.regExpProtect, function(m) {
                return '\\' + m;
            });
        } else {
            try {
                new RegExp(value);
            } catch (error) {
                me.statusBar.setStatus({
                    text: error.message,
                    iconCls: 'x-status-error'
                });
                return null;
            }
            // this is stupid
            if (value === '^' || value === '$') {
                return null;
            }
        }

        return value;
    }