fix runtime crash: you can't cast long to String

[D00mch]

Tests was not passing without this and I also checked it with

Convex convex = Convex.connect("https://convex.world");
Address address = convex.useNewAccount(30000);
AKeyPair keyPair = convex.getKeyPair();
Map<String, Object> queryResult = convex.queryAccount();
System.out.println(queryResult);