getEnv(): Return std::optional

This allows distinguishing between an empty value and no value.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 7d3da1cc8..842980fb7 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -870,11 +870,11 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 
 void LocalStore::autoGC(bool sync)
 {
-    static auto fakeFreeSpaceFile = getEnv("_NIX_TEST_FREE_SPACE_FILE", "");
+    static auto fakeFreeSpaceFile = getEnv("_NIX_TEST_FREE_SPACE_FILE");
 
     auto getAvail = [this]() -> uint64_t {
-        if (!fakeFreeSpaceFile.empty())
-            return std::stoll(readFile(fakeFreeSpaceFile));
+        if (fakeFreeSpaceFile)
+            return std::stoll(readFile(*fakeFreeSpaceFile));
 
         struct statvfs st;
         if (statvfs(realStoreDir.c_str(), &st))