title: predicateWithBlock as the predicate for ABPeoplePicker.predicateForEnablingPerson causes exception
body: <p>iOS8 introduced a new scheme for configuring ABPeoplePicker using NSPredicates. I need more than the a basic predicate for which people to enable so I tried using predicateWithBlock like so:</p>
  
  <pre><code>- (NSPredicate *)predicateForEnablingPerson
  {
      return [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings)
      {
          return TRUE; // Just pass back true until we figure out why it's crashing
      }];
  }   
  </code></pre>
  
  <p>There's nothing in the scant <a href="https://developer.apple.com/library/ios/documentation/addressbookui/reference/ABPeoplePickerNavigationController_Class/index.html#//apple_ref/occ/instp/ABPeoplePickerNavigationController/predicateForSelectionOfPerson" rel="nofollow">documentation</a> about this not being supported. Anyone know why this doesn't work?</p>
  
  <pre><code>thread #1: tid = 0x4b596e, 0x049cea6b libobjc.A.dylib`objc_exception_throw, name = 'MAINTHREAD-1412492637.228968-5', queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
          frame #0: 0x049cea6b libobjc.A.dylib`objc_exception_throw
          frame #1: 0x04e0bd1d CoreFoundation`+[NSException raise:format:] + 141
          frame #2: 0x03fadf0a Foundation`-[NSBlockPredicate encodeWithCoder:] + 59
          frame #3: 0x03ed9219 Foundation`-[NSXPCEncoder _encodeObject:] + 665
          frame #4: 0x03eeab49 Foundation`-[NSXPCEncoder _encodeArrayOfObjects:forKey:] + 299
          frame #5: 0x03ebe0a4 Foundation`-[NSDictionary(NSDictionary) encodeWithCoder:] + 1273
          frame #6: 0x03ed9219 Foundation`-[NSXPCEncoder _encodeObject:] + 665
          frame #7: 0x03eeab49 Foundation`-[NSXPCEncoder _encodeArrayOfObjects:forKey:] + 299
          frame #8: 0x03ebe0a4 Foundation`-[NSDictionary(NSDictionary) encodeWithCoder:] + 1273
          frame #9: 0x03ed9219 Foundation`-[NSXPCEncoder _encodeObject:] + 665
          frame #10: 0x03ed88c6 Foundation`-[NSXPCEncoder encodeObject:forKey:] + 135
          frame #11: 0x03ed9611 Foundation`-[NSXPCEncoder encodeObject:] + 48
          frame #12: 0x03ecd082 Foundation`_walkAndEncodeData + 1286
          frame #13: 0x03ecca8c Foundation`encodeInvocationArguments + 612
          frame #14: 0x03ed93dc Foundation`-[NSXPCEncoder encodeInvocation:] + 406
          frame #15: 0x03ed9219 Foundation`-[NSXPCEncoder _encodeObject:] + 665
          frame #16: 0x03ed88c6 Foundation`-[NSXPCEncoder encodeObject:forKey:] + 135
          frame #17: 0x03ed7c30 Foundation`-[NSXPCConnection _sendInvocation:proxyNumber:remoteInterface:withErrorHandler:timeout:userInfo:] + 2910
          frame #18: 0x03ee3668 Foundation`-[NSXPCConnection _sendInvocation:proxyNumber:remoteInterface:withErrorHandler:] + 95
          frame #19: 0x03ee35f9 Foundation`-[_NSXPCDistantObjectWithError forwardInvocation:] + 133
          frame #20: 0x04d5c78e CoreFoundation`___forwarding___ + 478
          frame #21: 0x04d5c58e CoreFoundation`__forwarding_prep_0___ + 14
          frame #22: 0x017515f4 AddressBookUI`-[CNContactPickerExtensionHostContext setupWithOptions:readyBlock:] + 312
          frame #23: 0x01750fca AddressBookUI`-[CNContactPickerHostViewController setupWithOptions:readyBlock:] + 166
          frame #24: 0x0166f4e5 AddressBookUI`-[CNContactPicker _setupViewController] + 1179
          frame #25: 0x0166f024 AddressBookUI`-[CNContactPicker _setViewController:] + 447
          frame #26: 0x0166f9a1 AddressBookUI`__41-[CNContactPicker _prepareViewController]_block_invoke116 + 72
          frame #27: 0x01750ddc AddressBookUI`__55+[CNContactPickerHostViewController getViewController:]_block_invoke + 340
          frame #28: 0x0322167e UIKit`__117-[NSExtension(UIViewControllerAdditions) instantiateViewControllerWithInputItems:listenerEndpoint:connectionHandler:]_block_invoke_3 + 129
          frame #29: 0x033723aa UIKit`__124+[_UIRemoteViewController _requestViewController:traitCollection:fromServiceWithBundleIdentifier:service:connectionHandler:]_block_invoke_2 + 107
          frame #30: 0x0528e41a libdispatch.dylib`_dispatch_call_block_and_release + 15
          frame #31: 0x052aee1f libdispatch.dylib`_dispatch_client_callout + 14
          frame #32: 0x05295981 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 610
          frame #33: 0x04d65f3e CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 14
          frame #34: 0x04d24d40 CoreFoundation`__CFRunLoopRun + 2256
          frame #35: 0x04d241ab CoreFoundation`CFRunLoopRunSpecific + 443
          frame #36: 0x04d23fdb CoreFoundation`CFRunLoopRunInMode + 123
          frame #37: 0x0661d24f GraphicsServices`GSEventRunModal + 192
          frame #38: 0x0661d08c GraphicsServices`GSEventRun + 104
          frame #39: 0x02c8de16 UIKit`UIApplicationMain + 1526
        * frame #40: 0x00002775 SmartRoam`main(argc=3, argv=0xbfffe4a4) + 565 at main.m:42
          frame #41: 0x052daac9 libdyld.dylib`start + 1
  </code></pre>