fix getBlanksSql() (#7549)

#### Rationale
fix getBlankSql()
[issue #1033
](LabKey/internal-issues#1033)

#### Related Pull Requests
- <!-- list of links to related pull requests (replace this comment) -->

#### Changes
- <!-- list of descriptions of changes that are worth noting (replace
this comment) -->


#### Tasks 📍
- [x] Needs Automation

Author: labkey-matthewb

api/src/org/labkey/api/exp/property/AbstractDomainKind.java

@@ -206,7 +206,7 @@ protected boolean getBlanksSql(Domain domain, DomainProperty prop, SQLFragment b
         else
         {
             // Issue 29047
-            blankRowsSQL.appendIdentifier(columnId).append(" IS NOT NULL");
+            blankRowsSQL.appendIdentifier(columnId).append(" IS NULL");
         }
         if (prop.isMvEnabled())
         {