Problems with custom fields

[Peter Sylvester]

There must be something I am missing :(

//Get issue "TNP-11"

var tnp11 = await _jira.Issues.GetIssueAsync("TNP-11");

var customFields = tnp11.CustomFields;
var a = customFields["Rank"];  //this works fine, I get the right object in a
var b = custFields["IssueLinkId"]; //this DOES NOT work, variable b will be null

var c = tnp11.CustomFields.FirstOrDefault(f => f.Name == "IssueLinkId"); //this works again

Why is 'b' null while 'c' is not?

Seemingly the [] operator has an issue with my custom field name "IssueLinkId".

thanks for your help 

[Peter Sylvester]

Seems that this problem happens only for NextGen projects :(

The RestAPI for custom fields seems to have a bug.

Where should I report this?