should return error

[usernameisnull]

if not return error, sometimes the program invoke this may panic

[yawuliu]

Jul 26 19:32:12 [1354154]: panic: runtime error: invalid memory address or nil pointer dereference Jul 26 19:32:12 [1354154]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0xafd118] Jul 26 19:32:12 [1354154]: goroutine 7767161 [running]: Jul 26 19:32:12 [1354154]: xxx/gojenkins.(*Requester).SetCrumb(0xc0009aed40, {0x17cf6b0, 0x1ff94e0}, 0xc039615d58) Jul 26 19:32:12 [1354154]: xxx/gojenkins/request.go:69 +0xb8
May leading to a probability panic if without this patch.