Merge pull request #29104 from duglin/Issue29084

Fix processing of unset build-args during build

api/types/client.go

@@ -160,10 +160,13 @@ type ImageBuildOptions struct {
 	ShmSize        int64
 	Dockerfile     string
 	Ulimits        []*units.Ulimit
-	BuildArgs      map[string]string
-	AuthConfigs    map[string]AuthConfig
-	Context        io.Reader
-	Labels         map[string]string
+	// See the parsing of buildArgs in api/server/router/build/build_routes.go
+	// for an explaination of why BuildArgs needs to use *string instead of
+	// just a string
+	BuildArgs   map[string]*string
+	AuthConfigs map[string]AuthConfig
+	Context     io.Reader
+	Labels      map[string]string
 	// squash the resulting image's layers to the parent
 	// preserves the original image and creates a new one from the parent with all
 	// the changes applied to a single layer