Regression: yaml tests break JRuby hard

jruby test/test_yaml.rb

Loaded suite test/test_yaml
Started
..................Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: -1, Size: 0
        at java.util.LinkedList.entry(LinkedList.java:382)
        at java.util.LinkedList.get(LinkedList.java:332)
        at org.jvyamlb.ScannerImpl.lastTokenIsFlowControl(ScannerImpl.java:494)
        at org.jvyamlb.ScannerImpl.fetchMoreTokens(ScannerImpl.java:512)
        at org.jvyamlb.ScannerImpl.peekToken(ScannerImpl.java:410)
        at org.jvyamlb.ScannerImpl.peekToken(ScannerImpl.java:416)
        at org.jvyamlb.ParserImpl$ProductionEnvironment.produce(ParserImpl.java:408)
        at org.jvyamlb.ParserImpl.parseStreamNext(ParserImpl.java:766)
        at org.jvyamlb.ParserImpl.peekEvent(ParserImpl.java:717)
        at org.jvyamlb.ComposerImpl.composeNode(ComposerImpl.java:89)
        at org.jvyamlb.ComposerImpl.composeNode(ComposerImpl.java:145)
        at org.jvyamlb.ComposerImpl.composeNode(ComposerImpl.java:145)
        at org.jvyamlb.ComposerImpl.composeDocument(ComposerImpl.java:78)
        at org.jvyamlb.ComposerImpl.getNode(ComposerImpl.java:54)
        at org.jvyamlb.BaseConstructorImpl.getData(BaseConstructorImpl.java:74)
        at org.jruby.RubyYAML.load(RubyYAML.java:200)
        at org.jruby.RubyYAMLInvoker$load_s_method_1_0.call(Unknown Source)
        at org.jruby.runtime.CallSite$InlineCachingCallSite.call(CallSite.java:329)
        at ruby.opt.work.jruby_dot_git.test.test_yaml.method__8$RUBY$assert_parse_only(test/test_yaml.rb:60)
        at ruby.opt.work.jruby_dot_git.test.test_yamlInvokermethod__8$RUBY$assert_parse_onlyFixed2.call(Unknown Source)
        at org.jruby.internal.runtime.methods.CompiledMethod.call(CompiledMethod.java:56)
        at org.jruby.runtime.CallSite$InlineCachingCallSite.cacheAndCall(CallSite.java:187)
        at org.jruby.runtime.CallSite$InlineCachingCallSite.call(CallSite.java:366)
        at ruby.opt.work.jruby_dot_git.test.test_yaml.method__50$RUBY$test_spec_builtin_map(test/test_yaml.rb:874)
        at ruby.opt.work.jruby_dot_git.test.test_yamlInvokermethod__50$RUBY$test_spec_builtin_mapFixed0.call(Unknown Source)
        at ruby.opt.work.jruby_dot_git.test.test_yamlInvokermethod__50$RUBY$test_spec_builtin_mapFixed0.call(Unknown Source)
        at org.jruby.RubyObject.send(RubyObject.java:2057)
        at org.jruby.RubyObjectInvoker$send_method_0_0.call(Unknown Source)
        at org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:78)