code: public ReplicationFilter compilePushReplicationFilter() {
          if (isPull())
              return null;
  
          if (filterName != null)
              return db.getFilter(filterName);
          else if (documentIDs != null && documentIDs.size() > 0) {
              final List<String> docIDs = documentIDs;
              return new ReplicationFilter() {
                  @Override
                  public boolean filter(SavedRevision revision, Map<String, Object> params) {
                      return docIDs.contains(revision.getDocument().getId());
                  }
              };
          }
          return null;
      }
docs: Get replicator filter. If the replicator is a pull replicator,
  calling this method will return null.
  <p/>
  This is equivalent to CBL_ReplicatorSettings's compilePushFilterForDatabase:status:.