command/build: Say if no artifacts were created

command/build/command.go

@@ -250,6 +250,8 @@ func (c Command) Run(env packer.Environment, args []string) int {
 				env.Ui().Say(message.String())
 			}
 		}
+	} else {
+		env.Ui().Say("\n==> Builds finished but no artifacts were created.")
 	}
 
 	return 0

packer/build.go

@@ -155,7 +155,7 @@ func (b *coreBuild) Run(ui Ui, cache Cache) ([]Artifact, error) {
 
 	builderArtifact, err := b.builder.Run(ui, hook, cache)
 	if err != nil {
-		return artifacts, err
+		return nil, err
 	}
 
 	errors := make([]error, 0)