code: public OClass probeOClass(int probeLimit) {
      	Iterator<ODocument> it = iterator(0, probeLimit, null);
      	return OSchemaUtils.probeOClass(it, probeLimit);
      }
docs: Probe the dataset and returns upper OClass for sample
  @param probeLimit size of a probe
  @return OClass or null if there is no common parent for {@link ODocument}'s in a sample