bug symfony#249 Fix unpack algo when requiring an unknown package (fa…

…bpot)

This PR was merged into the 1.0-dev branch.

Discussion
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Fix unpack algo when requiring an unknown package

fixes symfony#248

Commits
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5c5a08e fixed unpack algo when requiring an unknown package

src/Unpacker.php

@@ -40,6 +40,7 @@ public function unpack(Operation $op): Result
 
             // not unpackable or no --unpack flag or empty packs (markers)
             if (
+                null === $pkg ||
                 'symfony-pack' !== $pkg->getType() ||
                 !$op->shouldUnpack() ||
                 0 === count($pkg->getRequires()) + count($pkg->getDevRequires())