code: @Nullable
    public LookupExtractorFactoryMapContainer getLookup(final String tier, final String lookupName)
    {
      final Map<String, Map<String, LookupExtractorFactoryMapContainer>> prior = getKnownLookups();
      if (prior == null) {
        LOG.warn("Requested tier [%s] lookupName [%s]. But no lookups exist!", tier, lookupName);
        return null;
      }
      final Map<String, LookupExtractorFactoryMapContainer> tierLookups = prior.get(tier);
      if (tierLookups == null) {
        LOG.warn("Tier [%s] does not exist", tier);
        return null;
      }
      return tierLookups.get(lookupName);
    }
docs: Try to find a lookupName spec for the specified lookupName.
  
  @param lookupName The lookupName to look for
  
  @return The lookupName spec if found or null if not found or if no lookups at all are found