Filter nulls from select widget

resources/frontend_client/app/lib/schema_metadata.js

@@ -141,10 +141,12 @@ function equivalentArgument(field, table) {
             validValues.sort();
             return {
                 type: "select",
-                values: validValues.map(value => ({
-                    key: value,
-                    name: value
-                }))
+                values: validValues
+                    .filter(value => value != null)
+                    .map(value => ({
+                        key: value,
+                        name: value
+                    }))
             };
         }
     }

resources/frontend_client/app/query_builder/filters/FilterWidget.react.js

@@ -94,7 +94,6 @@ export default class FilterWidget extends Component {
             values = generateTimeFilterValuesDescriptions(this.props.filter);
         }
 
-        // the first 2 positions of the filter are always for fieldId + fieldOperator
         return values.map((value, valueIndex) => {
             var valueString = value != null ? value.toString() : null;
             return (