Fix: correct missing add field button for custom fields (#13424)

src-ui/src/app/components/manage/document-attributes/document-attributes.component.ts

@@ -163,12 +163,17 @@ export class DocumentAttributesComponent implements OnInit, OnDestroy {
   }
 
   get activeCustomFields(): CustomFieldsComponent | null {
-    if (this.activeSection?.kind !== DocumentAttributesSectionKind.CustomFields)
-      return null
+    if (!this.customFieldsActive) return null
     const instance = this.activeOutlet?.componentInstance
     return instance instanceof CustomFieldsComponent ? instance : null
   }
 
+  get customFieldsActive(): boolean {
+    return (
+      this.activeSection?.kind === DocumentAttributesSectionKind.CustomFields
+    )
+  }
+
   get activeTabLabel(): string {
     return this.activeSection?.label ?? ''
   }
@@ -224,6 +229,10 @@ export class DocumentAttributesComponent implements OnInit, OnDestroy {
     this.router.navigate(['attributes', nextSection])
   }
 
+  addCustomField(): void {
+    this.activeCustomFields?.editField(null)
+  }
+
   private getDefaultNavID(): DocumentAttributesNavIDs | null {
     return this.visibleSections[0]?.id ?? null
   }