diff --git a/docs/BUILD.bazel b/docs/BUILD.bazel
index 2bdbf6e..418dd13 100644
--- a/docs/BUILD.bazel
+++ b/docs/BUILD.bazel
@@ -97,7 +97,7 @@ set -euo pipefail
 short_commit="$${SHORT_COMMIT}"
 commit="$${COMMIT}"
 release="$${RELEASE}"
-if [[ -n "\\$${RELEASE}" ]]; then
+if [[ -n "\\$${RELEASE:-}" ]]; then
     release="\\$${RELEASE}"
 fi
 mkdir -p \\$${BUILD_WORKSPACE_DIRECTORY}/src