F null pointer list users

Summary

Fix for https://gitlab.com/linkahead/linkahead-server/-/issues/250

related: #334 (closed)

Focus

This is a minimal fix (just test for null before dereferencing).

Test Environment

Test in caosdb-cppinttest!33 (merged)

Also test manually with your customers setup, please

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src/main/java/org/caosdb/server/database/backend/implementation/MySQL/MySQLListUsers.java

@@ -54,7 +54,7 @@ public class MySQLListUsers extends MySQLTransaction implements ListUsersImpl {
           user.realm = rs.getString("realm");
           user.email = rs.getString("email");
           user.entity = rs.getString("entity");
-          if (user.entity.isBlank() || user.entity.equals("0")) {
+          if (user.entity == null || user.entity.isBlank() || user.entity.equals("0")) {
             user.entity = null;
           }
           user.status = UserStatus.valueOf(rs.getString("status"));