fix: return error instead of panicking when GetInfo resolves a nil repository

github/githubclient/client.go

@@ -200,6 +200,7 @@ func (c *client) GetInfo(ctx context.Context, gitcmd git.GitInterface) *github.G
 			c.config.Repo.GitHubRepoOwner,
 			c.config.Repo.GitHubRepoName)
 		check(err)
+		check(checkRepository(resp.Repository == nil, c.config.Repo.GitHubRepoOwner, c.config.Repo.GitHubRepoName))
 		pullRequestConnection = resp.Viewer.PullRequests
 		loginName = resp.Viewer.Login
 		repoID = resp.Repository.Id
@@ -208,6 +209,7 @@ func (c *client) GetInfo(ctx context.Context, gitcmd git.GitInterface) *github.G
 			c.config.Repo.GitHubRepoOwner,
 			c.config.Repo.GitHubRepoName)
 		check(err)
+		check(checkRepository(resp.Repository == nil, c.config.Repo.GitHubRepoOwner, c.config.Repo.GitHubRepoName))
 		pullRequestConnection = resp.Viewer.PullRequests
 		loginName = resp.Viewer.Login
 		repoID = resp.Repository.Id
@@ -842,6 +844,17 @@ func computeRequiredCheckStatus(contexts []checkContextNode, requiredChecks map[
 	return github.CheckStatusPass
 }
 
+// checkRepository returns an error when the GitHub GraphQL query resolved the
+// repository to null. The API returns a nil repository (sometimes without a
+// top-level error) when the token cannot access the repository or the
+// owner/name is wrong, and dereferencing it would panic.
+func checkRepository(isNil bool, owner, name string) error {
+	if isNil {
+		return fmt.Errorf("repository %s/%s not found; check the repository name and that GITHUB_TOKEN has access to it", owner, name)
+	}
+	return nil
+}
+
 func check(err error) {
 	if err != nil {
 		msg := err.Error()

github/githubclient/client_test.go

@@ -753,3 +753,12 @@ func TestComputeRequiredCheckStatus(t *testing.T) {
 		})
 	}
 }
+
+func TestCheckRepository(t *testing.T) {
+	err := checkRepository(false, "ejoffe", "spr")
+	require.NoError(t, err)
+
+	err = checkRepository(true, "ejoffe", "spr")
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "ejoffe/spr")
+}