From 90681986feab68ee1e3940d87ad07549bf8da2ff Mon Sep 17 00:00:00 2001
From: Martin Bruse <zondolfin@gmail.com>
Date: Wed, 26 Feb 2014 14:18:09 +0100
Subject: [PATCH] More discriminate env setting

---
 pkg/build/build.go | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/pkg/build/build.go b/pkg/build/build.go
index b95d75dd6..812844521 100644
--- a/pkg/build/build.go
+++ b/pkg/build/build.go
@@ -414,10 +414,18 @@ func (b *Builder) writeDockerfile(dir string) error {
 
 	dockerfile.WriteEnv("CI", "true")
 	dockerfile.WriteEnv("DRONE", "true")
-	dockerfile.WriteEnv("DRONE_BRANCH", b.Repo.Branch)
-	dockerfile.WriteEnv("DRONE_COMMIT", b.Repo.Commit)
-	dockerfile.WriteEnv("DRONE_PR", b.Repo.PR)
-	dockerfile.WriteEnv("DRONE_BUILD_DIR", b.Repo.Dir)
+	if b.Repo.Branch != "" {
+		dockerfile.WriteEnv("DRONE_BRANCH", b.Repo.Branch)
+	}
+	if b.Repo.Commit != "" {
+		dockerfile.WriteEnv("DRONE_COMMIT", b.Repo.Commit)
+	}
+	if b.Repo.PR != "" {
+		dockerfile.WriteEnv("DRONE_PR", b.Repo.PR)
+	}
+	if b.Repo.Dir != "" {
+		dockerfile.WriteEnv("DRONE_BUILD_DIR", b.Repo.Dir)
+	}
 
 	dockerfile.WriteAdd("proxy.sh", "/etc/drone.d/")
 	dockerfile.WriteEntrypoint("/bin/bash -e /usr/local/bin/drone")