👷 Fixes for truffleruby & jruby

Author: pboling

spec/oauth2/strategy/assertion_spec.rb

@@ -129,7 +129,7 @@
             # this behavior is handled by the JWT gem, but this should make sure it is consistent
             # On old Ruby (versions 2.4 and below) the error raised was different because
             #   an old version (< v2.4) of the jwt gem gets installed.
-            if Gem::Version.create(JWT::VERSION::STRING) >= Gem::Version.create("2.4")
+            if defined?(JWT::VERSION::STRING) && Gem::Version.create(JWT::VERSION::STRING) >= Gem::Version.create("2.4")
               expect { client_assertion.get_token(claims, encoding_opts) }.to raise_error(JWT::EncodeError, "Unsupported signing method")
             else
               expect { client_assertion.get_token(claims, encoding_opts) }.to raise_error(NotImplementedError)