code: private FSEditLogOp ingestFSEdit(EditLogInputStream inputEditLog)
        throws IOException {
      FSEditLogOp op = null;
      try {
        op = inputEditLog.readOp();
        InjectionHandler.processEventIO(InjectionEvent.INGEST_READ_OP);
      } catch (EOFException e) {
        return null; // No more transactions.
      } catch (IOException e) {
        // rethrow, it's handled in ingestFSEdits()
        throw e;
      } catch (Exception e) {
        // some other problem, maybe unchecked exception
        throw new IOException(e);
      }
      return op;
    }
docs: Read a single transaction from the input edit log
  @param inputEditLog the log to read from
  @return a single edit log entry, null if EOF
  @throws IOException on error