Null values chart

[lukavdplas]

The corpus information page shows what percentage of documents has a null value for each field over the entire corpus. It would be nice if this was also included as a visualisation type (similar to the "number of results"). For metadata fields with a coverage of, say, 50%, this can essentially answer the question which 50%. It could provide a lot of clarity on the quality of the data.

(It depends on the field whether such information can be inferred from the interface as it is, as null values can not be filtered/queried directly (in our interface). In some cases, you could infer this information with some clever searching, but you would at least have to subtract the values of multiple graphs.)