code: @Nullable
      public static MongoException fromThrowable(@Nullable final Throwable t) {
          if (t == null) {
              return null;
          } else {
              return fromThrowableNonNull(t);
          }
      }
docs: Static helper to create or cast a MongoException from a throwable
  
  @param t a throwable, which may be null
  @return a MongoException