fix: allow empty clause value when NE or CONTAINS

client/src/app/query/query.component.ts

@@ -878,17 +878,24 @@ export class QueryComponent
    */
   public hasInvalidCluase(clauses: any): boolean {
     for (let clause of clauses) {
+      clause['invalidClause'] = false
+
+      if (clause.value === '' &&
+          !(clause.operator === 'NE' ||
+          clause.operator === 'CONTAINS')) {
+        clause['invalidClause'] = true
+
+        return true
+      }
+
       if (
         clause.variable === null ||
         clause.operator === null ||
-        clause.value === null ||
-        clause.value === ''
+        clause.value === null
       ) {
         clause['invalidClause'] = true
 
         return true
-      } else {
-        clause['invalidClause'] = false
       }
     }