Returns whether two values are logically equal.
Similar to {@link #isEqual}, however null or undefined values will be treated as empty strings.
@private
@param {Object} value1 The first value to compare
@param {Object} value2 The second value to compare
@return {Boolean} True if the values are equal, false if inequal.
function(value1, value2){
        return String(Ext.value(value1, '')) === String(Ext.value(value2, ''));
    }