public async Task <string> GetGridSupplyPointByPostcodeAsync(string postcode) { var uri = ComposeGetGridSupplyPointByPostcodeUri(postcode); var result = await GetCollectionAsync <GridSupplyPoint>(uri); Debug.Assert(result != null); if (!result.Any()) { throw new GspException(Resources.NoGspFound); } if (result.Count() > 1) { throw new GspException(Resources.MultipleGspFound); } var gsp = result.Single().GroupId; Assertions.AssertValidGsp(gsp); return(gsp); }