Change useApiHolder to not throw when outside API context

Instead of throwing a NotImplementedError, useApiHolder now returns an
empty ApiHolder when no API context is available in the React tree.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/use-api-holder-no-throw.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-plugin-api': patch
+---
+
+Changed `useApiHolder` to return an empty `ApiHolder` instead of throwing when used outside of an API context.

packages/frontend-plugin-api/src/apis/system/useApi.test.tsx

@@ -17,7 +17,30 @@
 import { renderHook } from '@testing-library/react';
 import { createVersionedContextForTesting } from '@backstage/version-bridge';
 import { createApiRef } from './ApiRef';
-import { useApi } from './useApi';
+import { useApi, useApiHolder } from './useApi';
+
+describe('useApiHolder', () => {
+  const context = createVersionedContextForTesting('api-context');
+
+  afterEach(() => {
+    context.reset();
+  });
+
+  it('should return the API holder from context', () => {
+    const holder = { get: jest.fn() };
+    context.set({ 1: holder });
+
+    const renderedHook = renderHook(() => useApiHolder());
+    expect(renderedHook.result.current).toBe(holder);
+  });
+
+  it('should return an empty API holder when there is no context', () => {
+    const renderedHook = renderHook(() => useApiHolder());
+
+    const holder = renderedHook.result.current;
+    expect(holder.get(createApiRef<string>({ id: 'x' }))).toBeUndefined();
+  });
+});
 
 describe('useApi', () => {
   const context = createVersionedContextForTesting('api-context');

packages/frontend-plugin-api/src/apis/system/useApi.tsx

@@ -19,6 +19,8 @@ import { ApiRef, ApiHolder, TypesToApiRefs } from './types';
 import { useVersionedContext } from '@backstage/version-bridge';
 import { NotImplementedError } from '@backstage/errors';
 
+const emptyApiHolder: ApiHolder = { get: () => undefined };
+
 /**
  * React hook for retrieving {@link ApiHolder}, an API catalog.
  *
@@ -27,14 +29,10 @@ import { NotImplementedError } from '@backstage/errors';
 export function useApiHolder(): ApiHolder {
   const versionedHolder = useVersionedContext<{ 1: ApiHolder }>('api-context');
   if (!versionedHolder) {
-    throw new NotImplementedError('API context is not available');
+    return emptyApiHolder;
   }
 
-  const apiHolder = versionedHolder.atVersion(1);
-  if (!apiHolder) {
-    throw new NotImplementedError('ApiContext v1 not available');
-  }
-  return apiHolder;
+  return versionedHolder.atVersion(1) ?? emptyApiHolder;
 }
 
 /**