don't crash on invalid identifiers

fixes a bug where the link button would not be correctly disabled on invalid identifier values

(regression in 7015fae91c)

CHANGELOG.md

@@ -45,6 +45,7 @@ _Breaking developer changes, which may affect downstream projects or sites that
 #### :bug: Bugfixes
 * Validator: Don't falsely flag certain tags as "should be a closed area" if the tag also allows both area and line geometries in two separate presets (e.g. `highway=elevator` in the "Elevator" and "Inclined Lift" presets)
 * Fix sorting of nearby streets in address field dropdown
+* Fix bug where "outlink" buttons would not be disabled on invalid values of `identifier` fields
 #### :earth_asia: Localization
 #### :hourglass: Performance
 #### :mortar_board: Walkthrough / Help

modules/ui/fields/input.js

@@ -195,6 +195,7 @@ export function uiFieldText(field, context) {
                         window.open(url, '_blank');
                     }
                 })
+                .classed('disabled', () => !validIdentifierValueForLink())
                 .merge(outlinkButton);
         } else if (field.type === 'url') {
             input.attr('type', 'text');
@@ -375,7 +376,7 @@ export function uiFieldText(field, context) {
             }
         }
         if (field.type === 'identifier' && field.pattern) {
-            return value && value.match(new RegExp(field.pattern))[0];
+            return value && value.match(new RegExp(field.pattern))?.[0];
         }
         return null;
     }