code: public EnvelopeDocumentsResult updateDocuments(String accountId, String envelopeId, EnvelopeDefinition envelopeDefinition) throws ApiException {
      return updateDocuments(accountId, envelopeId, envelopeDefinition, null);
    }
docs: Adds one or more documents to an existing envelope document.
  Adds one or more documents to an existing envelope document.
  @param accountId The external account number (int) or account ID Guid. (required)
  @param envelopeId The envelopeId Guid of the envelope being accessed. (required)
  @param envelopeDefinition  (optional)
  @return EnvelopeDocumentsResult