How to set the filter for a field (varchar, yes NULL ) with empty value in Query Editor

Question

Hi there,

I have database table, one field "matnr" configured as varchar, can be NULL, but when setting it to null or NULL in the process model, then writing to database (pic 1), the field value is not NULL, while kind like empty (pic 2) . 
 I am trying to create a expression rule searching the information with this field "matnr" without value, set "matnr is null" is not working. what's the way to do this? why Appian condition "is null" in Query editor does not work for empty field as other languages? 
 regards, Lin

Mike Schmitt · Answer

This is a long-known "bug" of sorts with the way a!queryEntity works (unfortunately); but there's a relatively easy workaround once you know it - a!queryFilter(field: "matnr", operator: "=", value: " ") (that's an empty space ). So you'd make a queryLogicalExpression() entry with the "OR" operator doing this *and* the "is null" operator check. 
 (I have no idea what you'd do, however, if you wanted to find entries where the value of the field = "one empty space", but whatever.)