modules/image/repart: fix Format=empty (#561424)

nixos/modules/image/repart-image.nix

@@ -109,6 +109,7 @@ let
     "btrfs" = [ btrfs-progs ];
     "xfs" = [ xfsprogs ];
     "swap" = [ util-linux ];
+    "empty" = [ ];
   };
 
   fileSystemTools = builtins.concatMap (f: fileSystemToolMapping."${f}") fileSystems;

nixos/tests/appliance-repart-image.nix

@@ -90,7 +90,16 @@ in
               Minimize = "guess";
             };
           };
-        };
+        }
+        // (lib.genAttrs [ "squashfs" "erofs" "btrfs" "xfs" "swap" "empty" ] (fsType: {
+          repartConfig = {
+            Type = "linux-generic";
+            Format = fsType;
+
+            SizeMinBytes = "10M";
+            SizeMaxBytes = "10M";
+          };
+        }));
       };
     };