src/jdk.jpackage/share/classes/jdk/jpackage/internal/AddLauncherArguments.java

*** 162,167 ****
--- 162,185 ----
              String param, Map<?, ?> value) {
          if (value != null && !value.isEmpty()) {
              params.put(param, value);
          }
      }
+ 
+     static Map<String, ? super Object> merge(
+             Map<String, ? super Object> original,
+             Map<String, ? super Object> additional) {
+         Map<String, ? super Object> tmp = new HashMap<>(original);
+         if (additional.containsKey("module")) {
+             tmp.remove("main-jar");
+             tmp.remove("main-class");
+         } else if (additional.containsKey("main-jar")) {
+             tmp.remove("module");
+             // should we only remove add-modules when it wasn't actually passed
+             // but was inferred or empty ?
+             tmp.remove("add-modules");
+         }
+         tmp.putAll(additional);
+         return tmp;
+     }
+ 
  }