Response#issuer may be nil
Response#issuer may be nil

Change-Id: Id0d7ab0dd7314aa1aa8fa89e1c18bffda78a6361
Reviewed-on: https://gerrit.instructure.com/152336
Tested-by: Jenkins
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

instructure/ruby-saml2,instructure/ruby-saml2