code: public Csv nullLiteral(String nullLiteral) {
  		Preconditions.checkNotNull(nullLiteral);
  		internalProperties.putString(FORMAT_NULL_LITERAL, nullLiteral);
  		return this;
  	}
docs: Sets the null literal string that is interpreted as a null value (disabled by default).
  
  @param nullLiteral null literal (e.g. "null" or "n/a")