From ebf0194d51542024f29c47e676874ef34ec64c33 Mon Sep 17 00:00:00 2001
From: Tonis Tiigi <tonistiigi@gmail.com>
Date: Wed, 16 Sep 2020 19:36:16 -0700
Subject: [PATCH] client: allow build callback to return nil result

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
---
 frontend/gateway/grpcclient/client.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/frontend/gateway/grpcclient/client.go b/frontend/gateway/grpcclient/client.go
index b0a2b2d2..35a3fa3f 100644
--- a/frontend/gateway/grpcclient/client.go
+++ b/frontend/gateway/grpcclient/client.go
@@ -171,6 +171,10 @@ func (c *grpcClient) Run(ctx context.Context, f client.BuildFunc) (retError erro
 		return err
 	}
 
+	if res == nil {
+		return nil
+	}
+
 	if err := c.caps.Supports(pb.CapReturnMap); len(res.Refs) > 1 && err != nil {
 		return err
 	}