code: public <T> AsyncMutateInBuilder insert(String path, T fragment, SubdocOptionsBuilder optionsBuilder) {
          if (StringUtil.isNullOrEmpty(path)) {
              throw new IllegalArgumentException("Path must not be empty for insert");
          }
          this.mutationSpecs.add(new MutationSpec(Mutation.DICT_ADD, path, fragment, optionsBuilder));
          return this;
      }
docs: Insert a fragment, provided the last element of the path doesn't exist.
  
  @param path the path where to insert a new dictionary value.
  @param fragment the new dictionary value to insert.
  @param optionsBuilder {@link SubdocOptionsBuilder}