/**
  * <code>required .dossier.Index index = 3;</code>
  *
  * <pre>
  * Navigation index.
  * </pre>
  */
 public Builder mergeIndex(com.github.jsdossier.proto.Index value) {
   if (indexBuilder_ == null) {
     if (((bitField0_ & 0x00000004) == 0x00000004)
         && index_ != com.github.jsdossier.proto.Index.getDefaultInstance()) {
       index_ =
           com.github.jsdossier.proto.Index.newBuilder(index_).mergeFrom(value).buildPartial();
     } else {
       index_ = value;
     }
     onChanged();
   } else {
     indexBuilder_.mergeFrom(value);
   }
   bitField0_ |= 0x00000004;
   return this;
 }