private void warnIfDatabaseIsNotEmpty() {
    final long chainHeight =
        controller.getProtocolContext().getBlockchain().getChainHead().getHeight();
    if (chainHeight > BlockHeader.GENESIS_BLOCK_NUMBER) {
      LOG.warn(
          "Importing to a non-empty database with chain height {}.  This may cause imported blocks to be considered non-canonical.",
          chainHeight);
    }
  }
Import chain.

@param chainJson the chain json
@throws IOException the io exception
app/src/main/java/org/hyperledger/besu/chainimport/JsonBlockImporter.java