If a medication was not pre-specified the value of CMOCCUR should be null.
CMPRESP and CMOCCUR is a permissible fields and may be omitted from the dataset if all medications were collected as free text.
Values of CMOCCUR may also be null for pre-specified medications if no Y/N response was collected; in this case, CMSTAT = NOT DONE, and CMREASND could be used to describe the reason the answer was missing.