I'm sure I am being dumb but can anyone see why
```
fishOverlay = self: super: {
    fish = (super.pkgs.fish.overrideAttrs (old: {
      src = old.src.override {
        rev = "c6ec4235136e82c709e8d7b455f7c463f9714b48";
        sha256 = "0000000000000000000000000000000000000000000000000000";
      };
    }));
  };
```