feat(query): add isnull operator for NULL checks#528

joshdimanteto merged 3 commits intoremove-older-python-versions-#517ral-facilities/datagateway-api:remove-older-python-versions-#517from

add-isnull-where-filter-#527ral-facilities/datagateway-api:add-isnull-where-filter-#527Copy head branch name to clipboard