Fix transformer being run with empty config.

Now does nothing instead of erroring.

Author: LexManos

at-gradle/src/main/java/net/minecraftforge/accesstransformers/gradle/ArtifactAccessTransformer.java

@@ -205,7 +205,12 @@ private void exec(TransformOutputs outputs) throws Exception {
 
         // inputs
         var inJar = this.getInputArtifact().get().getAsFile();
-        var atFile = parameters.getConfig().map(RegularFile::getAsFile).get();
+        var atFile = parameters.getConfig().getAsFile().getOrNull();
+        if (atFile == null) {
+            // No config so just return the input file
+            outputs.file(inJar);
+            return;
+        }
 
         // outputs
         var outJarName = inJar.getName().replace(".jar", "-at.jar");