"na value" returned from lookup procedure

Hi experts,

My RPAS version is 13.2.2.37

Referring to Configuration Tolls User Guide, it says "When <map> contains index numbers that do not map to valid positions, an error is generated and the na value for <output> is returned".

In my case, when the <map> measure (type string) is a empty cell:

1) no error is generated, the mace utility ends successfully and no RPAS exception pops; is empty cell considered as a valid position?

2) empty is not found in <input> and na value is returned, but it seems RPAS returns na value of the db, instead that of Configuration; when na value