Update source_machine_config.go

builder/triton/source_machine_config.go

@@ -112,9 +112,7 @@ func (c *SourceMachineConfig) Prepare(ctx *interpolate.Context) []error {
 		c.MachineTags = make(map[string]string)
 	}
 
-	if len(errs) > 0 {
-		return errs
-	}
+	errs = append(errs, c.MachineTag.CopyOn(c.MachineTags)...)
 
-	return nil
+	return errs
 }