lib.hydraJob: Tolerate null

By allowing null, we allow code to avoid filterAttrs, improving
laziness in real world use cases.
Specifically, this strategy prevents infinite recursion errors,
performance issues and possibly other errors that are unrelated to
the user's code.

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/customisation.nix b/lib/customisation.nix
index 101c9e62b9e6..42d711cf5fb9 100644
--- a/lib/customisation.nix
+++ b/lib/customisation.nix
@@ -252,7 +252,8 @@ rec {
       outputsList = map makeOutput outputs;
 
       drv' = (lib.head outputsList).value;
-    in lib.deepSeq drv' drv';
+    in if drv == null then null else
+      lib.deepSeq drv' drv';
 
   /* Make a set of packages with a common scope. All packages called
      with the provided `callPackage` will be evaluated with the same