Handling NULL in dimensions and measures

A small post about 'Unknown' and 'Not Available' values in datawarehouse solutions. I've a requirement of my customer about this issue. The customer wants to see whether a value of a field in the sourcetable is empty (= NULL) or whether the value is not present in the dimension. There is a distinction between the two types of mismatching. The same problem is there with measures. They also want to see whether a measure value is NULL or whether it has a valid value. This way it's possible to monitor the dataquality of the source in a more sophisticated manner.