Make the diffPath optional

Author: serpent7776

bin/Main.ml

@@ -60,7 +60,7 @@ let main img1Path img2Path diffPath threshold outputDiffMask failOnLayoutChange
       ->
         { exitCode = 0; diff = Some diffOutput }
     | Pixel (diffOutput, diffCount, diffPercentage, _) ->
-        IO1.saveImage diffOutput diffPath;
+        diffPath |> Option.iter (IO1.saveImage diffOutput);
         { exitCode = 22; diff = Some diffOutput }
   in
   IO1.freeImage img1;

bin/ODiffBin.ml

@@ -3,8 +3,8 @@ open Term
 open Arg
 
 let diffPath =
-  value & pos 2 string ""
-  & info [] ~docv:"DIFF" ~doc:"Diff output path (.png only)"
+  value & pos 2 (some string) None
+  & info [] ~docv:"DIFF" ~doc:"Optional Diff output path (.png only)"
 
 let base =
   value & pos 0 file "" & info [] ~docv:"BASE" ~doc:"Path to base image"