code: public SoyType removeNullability() {
      if (isNullable()) {
        return of(
            members.stream()
                .filter(t -> t.getKind() != SoyType.Kind.NULL)
                .collect(Collectors.toList()));
      }
      return this;
    }
docs: Returns a Soy type that is equivalent to this one but with 'null' removed.