ci/eval/compare/maintainers: Handle nonexistent attribute in changedByNameAttrPaths (#499760)

ci/eval/compare/maintainers.nix

@@ -96,6 +96,8 @@ let
     (lib.filter (path: lib.length path > 3))
     (map (path: lib.elemAt path 3))
     (map lib.singleton)
+    # Filter out new packages
+    (lib.filter (attrPath: lib.hasAttrByPath attrPath pkgs))
   ];
 
   # An attribute can appear in affected *and* touched

ci/eval/compare/test.nix

@@ -138,6 +138,21 @@ let
         ];
       };
     };
+    testByNameNonExistentChanged = {
+      expr = fun {
+        pkgs = mockPkgs {
+          packages = [ ];
+        };
+        # Happens when a new package was added to pkgs/by-name
+        changedFiles = [ "pkgs/by-name/he/hello/sources.json" ];
+        affectedAttrPaths = [ ];
+      };
+      expected = {
+        packages = [ ];
+        teams = { };
+        users = { };
+      };
+    };
     testByNameReadmeChanged = {
       expr = fun {
         pkgs = mockPkgs {