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-rw-r--r--third_party/nix/src/libutil/util.hh2
1 files changed, 1 insertions, 1 deletions
diff --git a/third_party/nix/src/libutil/util.hh b/third_party/nix/src/libutil/util.hh
index b6d726b46c01..b3349c4f39c4 100644
--- a/third_party/nix/src/libutil/util.hh
+++ b/third_party/nix/src/libutil/util.hh
@@ -26,7 +26,7 @@ struct Source;
 extern const std::string nativeSystem;
 
 /* Return an environment variable. */
-std::string getEnv(const std::string& key, const std::string& def = "");
+std::optional<std::string> getEnv(const std::string& key);
 
 /* Get the entire environment. */
 std::map<std::string, std::string> getEnv();