just before readline(prompt)
irb(main):002:0> ^DNULL returned

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0xc000004d
0x000a387d in rubinius::TypedRoot<rubinius::Object*>::get (this=0xc0000045) at gc_root.hpp:232
232           return reinterpret_cast<ObjType>(object);
(gdb) bt 10
#0  0x000a387d in rubinius::TypedRoot<rubinius::Object*>::get (this=0xc0000045) at gc_root.hpp:232
#1  0x000c051d in rubinius::NativeMethodFrame::get_object (this=0xbffcd6b4, hndl=-3) at vm/builtin/nativemethod.cpp:37
#2  0x000c0c4c in rubinius::NativeMethod::call (this=0x11f5cb8, state=0x3001a0, frame=0xbffcd6b4, msg=@0xbffcd898) at vm/builtin/nativemethod.cpp:194
#3  0x000c1039 in rubinius::NativeMethod::executor_implementation (state=0x3001a0, call_frame=0xbffcef20, msg=@0xbffcd898) at vm/builtin/nativemethod.cpp:93
#4  0x000c588a in rubinius::performer::mono_performer (state=0x3001a0, call_frame=0xbffcef20, msg=@0xbffcd898) at vm/builtin/sendsite.cpp:29
#5  0x0010ed29 in rubinius::VMMethod::interpreter (state=0x3001a0, vmm=0x1a347e0, call_frame=0xbffcef20) at vm/gen/instructions.cpp:2539
#6  0x000a2396 in rubinius::VMMethod::run_interpreter (state=0x3001a0, vmm=0x1a347e0, call_frame=0xbffcef20) at vm/vmmethod.cpp:675
#7  0x000a51f0 in rubinius::VMMethod::execute_specialized<rubinius::GenericArguments> (state=0x3001a0, previous=0xbffd0930, msg=@0xbffcf2a8) at vm/vmmethod.cpp:501
#8  0x000c588a in rubinius::performer::mono_performer (state=0x3001a0, call_frame=0xbffd0930, msg=@0xbffcf2a8) at vm/builtin/sendsite.cpp:29
#9  0x0010ed29 in rubinius::VMMethod::interpreter (state=0x3001a0, vmm=0x1a2e000, call_frame=0xbffd0930) at vm/gen/instructions.cpp:2539
(More stack frames follow...)