Merge pull request #9930 from rvl/print-dev-env-unbound-variables

print-dev-env: Avoid using unbound shellHook variable
(cherry picked from commit 25385a408ef7281d966c8732608833e224b32586)
Change-Id: Id1aca13942adfa628f7bdcfc0b6fc03bb3bab9ea

src/nix/develop.cc

@@ -318,7 +318,7 @@ struct Common : InstallableCommand, MixProfile
         for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
             out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
 
-        out << "eval \"$shellHook\"\n";
+        out << "eval \"${shellHook:-}\"\n";
 
         auto script = out.str();