code: @Override
  	public FlatRateState getFlatRateState(String CorpNum, String UserID)
  			throws PopbillException {
  		return httpget("/HomeTax/Taxinvoice/Contract", CorpNum, UserID, FlatRateState.class);
  	}
docs: /*
  (non-Javadoc)
  @see com.popbill.api.HTTaxinvoiceService#GetFlatRateState(java.lang.String, java.lang.String)