Example code:

class IteratorEnumeration
  include Java::JavaUtil::Enumeration
  include Java::JavaUtil::Iterator

  def initialize(aIterator)
    @iterator = aIterator
  end

  def nextElement
    @iterator.next
  end

  alias :next_element nextElement

  def hasMoreElements
    @iterator.hasNext
  end

  def hasNext
    @iterator.hasNext
  end

  alias :has_next hasNext
  alias :has_next? hasNext

  def next
    @iterator.next
  end

  def remove
    @iterator.remove
  end

  alias :has_more_elements hasMoreElements
  alias :has_more_elements? hasMoreElements
end


linkedHashMap = Java::JavaUtil::LinkedHashMap.new
linkedHashMap.put('foo', 'foo')
linkedHashMap.put('bar', 'bar')
linkedHashMap.put('baz', 'baz')
iten = IteratorEnumeration.new(linkedHashMap.keySet.iterator)
puts 'start'
iten.each do |entry|
  puts entry
end
puts 'end'

Behavior in Jruby 9.0.5.0 (jruby 9.0.5.0 (2.2.3) 2016-01-26 7bee00d Java HotSpot(TM) 64-Bit Server VM 25.101-b13 on 1.8.0_101-b13 +jit [Windows 10-amd64])

c:\tools>jruby foo.rb
start
foo
bar
baz
end

Behavior in Jruby 9.1.4.0 (jruby 9.1.4.0 (2.3.1) 2016-09-01 2e1327f Java HotSpot(TM) 64-Bit Server VM 25.101-b13 on 1.8.0_101-b13 +jit [mswin32-x86_64])

c:\tools>jruby foo.rb

start
Unhandled Java exception: java.lang.NullPointerException
java.lang.NullPointerException: null
unwrapJavaObject at org/jruby/javasupport/JavaUtil.java:287
each at org/jruby/javasupport/ext/JavaUtil.java:104
call at org/jruby/javasupport/ext/JavaUtil$Iterator$INVOKER$s$0$0$each.gen:-1
cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:328
callBlock at org/jruby/runtime/callsite/CachingCallSite.java:141
call at org/jruby/runtime/callsite/CachingCallSite.java:145
invokeOther46:each at foo.rb:46

at foo.rb:46
invokeWithArguments at java/lang/invoke/MethodHandle.java:627
load at org/jruby/ir/Compiler.java:111
runScript at org/jruby/Ruby.java:834
runNormally at org/jruby/Ruby.java:749
runNormally at org/jruby/Ruby.java:767
runFromMain at org/jruby/Ruby.java:580
doRunFromMain at org/jruby/Main.java:425
internalRun at org/jruby/Main.java:313
run at org/jruby/Main.java:242
main at org/jruby/Main.java:204

Expected behavior is that Jruby 9.1.4.0 behaves as 9.0.5.0