Change error handling on ReadBranchConfig to respect git Exit Codes

git/client.go

@@ -392,12 +392,10 @@ func (c *Client) ReadBranchConfig(ctx context.Context, branch string) (BranchCon
 	out, err := cmd.Output()
 	if err != nil {
 		// This is the error we expect if the git command does not run successfully.
-		// Note: err is non-nil if the command is successful but has no output
+		// If the ExitCode is 1, then we just didn't find any config for the branch.
 		var gitError *GitError
-		if errors.As(err, &gitError) {
-			if gitError.Stderr != "" {
-				return BranchConfig{}, err
-			}
+		if ok := errors.As(err, &gitError); ok && gitError.ExitCode != 1 {
+			return BranchConfig{}, err
 		}
 		return BranchConfig{}, nil
 	}

git/client_test.go

@@ -744,16 +744,7 @@ func TestClientReadBranchConfig(t *testing.T) {
 			wantError:        nil,
 		},
 		{
-			name:             "output error",
-			cmdExitStatus:    1,
-			cmdStdout:        "",
-			cmdStderr:        "git error message",
-			branch:           "trunk",
-			wantBranchConfig: BranchConfig{},
-			wantError:        &GitError{},
-		},
-		{
-			name:             "git config runs successfully but returns no output",
+			name:             "git config runs successfully but returns no output (Exit Code 1)",
 			cmdExitStatus:    1,
 			cmdStdout:        "",
 			cmdStderr:        "",
@@ -761,6 +752,15 @@ func TestClientReadBranchConfig(t *testing.T) {
 			wantBranchConfig: BranchConfig{},
 			wantError:        nil,
 		},
+		{
+			name:             "output error (Exit Code > 1)",
+			cmdExitStatus:    2,
+			cmdStdout:        "",
+			cmdStderr:        "git error message",
+			branch:           "trunk",
+			wantBranchConfig: BranchConfig{},
+			wantError:        &GitError{},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {