Alternative fix: keep back compat with interceptor contract

client.go

@@ -95,7 +95,7 @@ func NewClient[Req, Res any](httpClient HTTPClient, url string, options ...Clien
 		response, err := receiveUnaryResponse[Res](conn, config.Initializer)
 		if err != nil {
 			_ = conn.CloseResponse()
-			return response, err
+			return nil, err
 		}
 		return response, conn.CloseResponse()
 	})
@@ -110,7 +110,7 @@ func NewClient[Req, Res any](httpClient HTTPClient, url string, options ...Clien
 		request.peer = client.protocolClient.Peer()
 		protocolClient.WriteRequestHeader(StreamTypeUnary, request.Header())
 		response, err := unaryFunc(ctx, request)
-		if err != nil {
+		if err != nil || response == nil {
 			return nil, err
 		}
 		typed, ok := response.(*Response[Res])

client_error_handling_test.go

@@ -53,7 +53,7 @@ func TestClientErrorHandling(t *testing.T) {
 
 // errorHidingInterceptor is a simple interceptor that hides errors based on
 // some criteria (in this case, if the error is a CodeCanceled error). It is
-// use to reproduce an issue with error handling in the client, where the
+// used to reproduce an issue with error handling in the client, where the
 // type information is lost between unaryFunc and client.callUnary.
 type errorHidingInterceptor struct{}