public static String getString(
      final ObjectNode node, final String key, final String defaultValue) {
    return getString(node, key).orElse(defaultValue);
  }
Returns textual (string) value at {@code key}. See {@link #getValueAsString} for retrieving
non-textual values in string form.

@param node The {@code ObjectNode} from which the value will be extracted.
@param key The key corresponding to the value to extract.
@param defaultValue The value to return if no value is found at {@code key}.
@return The textual value at {@code key} if it exists, otherwise {@code defaultValue}
config/src/main/java/org/hyperledger/besu/config/JsonUtil.java