message: make event handelers nullable
diff: @@ -723,7 +723,7 @@ function EmitWebIDl(webidl: Browser.WebIdl, flavor: Flavor) {
  }
  }
  let requiredModifier = !p.required || p.required === "1" ? "" : "?";
  - //pType = p.nullable ? makeNullable(pType) : pType;
  + pType = p.nullable ? makeNullable(pType) : pType;
  let readOnlyModifier = p["read-only"] && prefix === "" ? "readonly " : "";
  printLine(`${prefix}${readOnlyModifier}${p.name}${requiredModifier}: ${pType};`);
  }
  