以下行与EXC_BAD_ACCESS（下面的堆栈跟踪）可靠地崩溃：
self.addressBookContacts.sortInPlace({ $0.contactTitle < $1.contactTitle })
我不会提供任何背景信息，因为我不认为问题出在我的代码上。我这样说是因为：
a）此异常仅在我构建Release配置时发生。调试很好。
b）当我用下面的代替这一行时，不再有崩溃：
self.addressBookContacts = self.addressBookContacts.sort({$0.contactTitle < $1.contactTitle})
有什么可以解释这种行为，我该如何调试呢？
* thread #1: tid = 0x380248, 0x0000000199f140b0 libobjc.A.dylib`objc_retain + 16, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x20)
frame #0: 0x0000000199f140b0 libobjc.A.dylib`objc_retain + 16
* frame #1: 0x0000000100147294 MyApp`MyApp.AddressBookContact.contactTitle.getter : Swift.Optional<Swift.String>(self=<unavailable>) + 56 at Contactable.swift:45 [opt]
frame #2: 0x0000000100203ba8 MyApp`function signature specialization <Arg[0] = Owned To Guaranteed, Arg[1] = Owned To Guaranteed> of MyApp.RequestRecommendationsViewController.($0=<unavailable>, $1=(null) at x20) (MyApp.RequestRecommendationsViewController) -> () -> ()).(closure #2).(closure #1) + 36 at RequestRecommendationsViewController.swift:112 [opt]
frame #3: 0x00000001001fe600 MyApp`function signature specialization <Arg[0] = [Constant Propagated Function : MyApp.RequestRecommendationsViewController.((populateAddressBookContacts in _741B2008EB467CE4CB3AD995A528F38A) (MyApp.RequestRecommendationsViewController) -> () -> ()).(closure #2).(closure #1)]> of reabstraction thunk helper from @callee_owned (@owned MyApp.AddressBookContact, @owned MyApp.AddressBookContact) -> (@unowned Swift.Bool) to @callee_owned (@in MyApp.AddressBookContact, @in MyApp.AddressBookContact) -> (@unowned Swift.Bool) + 36 at RequestRecommendationsViewController.swift:0 [opt]
frame #4: 0x0000000100201a4c MyApp`generic specialization <Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> with Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> with Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> with Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.Indexable in Swift and Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> with Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>, MyApp.AddressBookContact, MyApp.AddressBookContact> of Swift._partition <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A, Swift.Range<A.Index>, inout (A.Generator.Element, A.Generator.Element) -> Swift.Bool) -> A.Index + 188 at RequestRecommendationsViewController.swift:0 [opt]
frame #5: 0x0000000100200b68 MyApp`generic specialization <Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> with Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> with Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> with Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.Indexable in Swift and Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> with Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>, MyApp.AddressBookContact, MyApp.AddressBookContact> of Swift._introSortImpl <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A, Swift.Range<A.Index>, inout (A.Generator.Element, A.Generator.Element) -> Swift.Bool, Swift.Int) -> () + 392 at RequestRecommendationsViewController.swift:0 [opt]
frame #6: 0x0000000100200b88 MyApp`generic specialization <Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> with Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> with Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> with Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.Indexable in Swift and Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> with Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>, MyApp.AddressBookContact, MyApp.AddressBookContact> of Swift._introSortImpl <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A, Swift.Range<A.Index>, inout (A.Generator.Element, A.Generator.Element) -> Swift.Bool, Swift.Int) -> () + 424 at RequestRecommendationsViewController.swift:0 [opt]
frame #7: 0x0000000100200744 MyApp`generic specialization <Swift.Array<MyApp.AddressBookContact> with Swift.Array<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact> with Swift.ArraySlice<MyApp.AddressBookContact> : Swift.Indexable in Swift and Swift.ArraySlice<MyApp.AddressBookContact> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact>, MyApp.AddressBookContact, MyApp.AddressBookContact> of ext.Swift.Swift.MutableCollectionType<A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType>.(sortInPlace <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A) -> ((A.Generator.Element, A.Generator.Element) -> Swift.Bool) -> ()).(closure #1) [inlined] generic specialization <Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> with Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> with Swift.UnsafeBufferPointerGenerator<MyApp.AddressBookContact> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> with Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.Indexable in Swift and Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> with Swift.IndexingGenerator<Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.MutableSlice<Swift.UnsafeMutableBufferPointer<MyApp.AddressBookContact>>, MyApp.AddressBookContact, MyApp.AddressBookContact> of Swift._introSort <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A, Swift.Range<A.Index>, (A.Generator.Element, A.Generator.Element) -> Swift.Bool) -> () + 8 at RequestRecommendationsViewController.swift:0 [opt]
frame #8: 0x000000010020073c MyApp`generic specialization <Swift.Array<MyApp.AddressBookContact> with Swift.Array<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact> with Swift.ArraySlice<MyApp.AddressBookContact> : Swift.Indexable in Swift and Swift.ArraySlice<MyApp.AddressBookContact> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact>, MyApp.AddressBookContact, MyApp.AddressBookContact> of ext.Swift.Swift.MutableCollectionType<A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType>.(sortInPlace <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A) -> ((A.Generator.Element, A.Generator.Element) -> Swift.Bool) -> ()).(closure #1) + 120 at RequestRecommendationsViewController.swift:0 [opt]
frame #9: 0x00000001001fdd7c MyApp`_TPA__TTSg5GSaC8MyApp18AddressBookContact_GSaS0__Ss21MutableCollectionTypeSs_GVSs17IndexingGeneratorGSaS0___GS2_GSaS0___Ss13GeneratorTypeSs_S0__SiSiSs21RandomAccessIndexTypeSs_SiSiSs18_SignedIntegerTypeSs_SiSiSs33_BuiltinIntegerLiteralConvertibleSs_SiSiSs16SignedNumberTypeSs_SiSiS6_Ss_Si_GVSs10ArraySliceS0__GS8_S0__Ss9IndexableSsGS8_S0__Ss12SequenceTypeSs_GS2_GS8_S0___GS2_GS8_S0___S3_Ss_S0__SiSiSs16ForwardIndexTypeSs_SiSiS5_Ss_SiSiS6_Ss_Si_GS8_S0___S0__S0____TTRGRq_Ss21MutableCollectionTypeqq_Ss16MutableIndexable5IndexSs21RandomAccessIndexType_XFo_dGVSs20UnsafeMutablePointerqqq_Ss14CollectionType9GeneratorSs13GeneratorType7Element_dSi_dT_zoPSs9ErrorType__XFo_dGS2_qqq_S3_9GeneratorS4_7Element_dSi_iT_zoPS5___ [inlined] generic specialization <Swift.Array<MyApp.AddressBookContact> with Swift.Array<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact> with Swift.ArraySlice<MyApp.AddressBookContact> : Swift.Indexable in Swift and Swift.ArraySlice<MyApp.AddressBookContact> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact>, MyApp.AddressBookContact, MyApp.AddressBookContact> of reabstraction thunk helper <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> from @callee_owned (@unowned Swift.UnsafeMutablePointer<A.Generator.Element>, @unowned Swift.Int) -> (@unowned (), @error @owned Swift.ErrorType) to @callee_owned (@unowned Swift.UnsafeMutablePointer<A.Generator.Element>, @unowned Swift.Int) -> (@out (), @error @owned Swift.ErrorType) + 20 at RequestRecommendationsViewController.swift:0 [opt]
frame #10: 0x00000001001fdd68 MyApp`_TPA__TTSg5GSaC8MyApp18AddressBookContact_GSaS0__Ss21MutableCollectionTypeSs_GVSs17IndexingGeneratorGSaS0___GS2_GSaS0___Ss13GeneratorTypeSs_S0__SiSiSs21RandomAccessIndexTypeSs_SiSiSs18_SignedIntegerTypeSs_SiSiSs33_BuiltinIntegerLiteralConvertibleSs_SiSiSs16SignedNumberTypeSs_SiSiS6_Ss_Si_GVSs10ArraySliceS0__GS8_S0__Ss9IndexableSsGS8_S0__Ss12SequenceTypeSs_GS2_GS8_S0___GS2_GS8_S0___S3_Ss_S0__SiSiSs16ForwardIndexTypeSs_SiSiS5_Ss_SiSiS6_Ss_Si_GS8_S0___S0__S0____TTRGRq_Ss21MutableCollectionTypeqq_Ss16MutableIndexable5IndexSs21RandomAccessIndexType_XFo_dGVSs20UnsafeMutablePointerqqq_Ss14CollectionType9GeneratorSs13GeneratorType7Element_dSi_dT_zoPSs9ErrorType__XFo_dGS2_qqq_S3_9GeneratorS4_7Element_dSi_iT_zoPS5___ + 56 at RequestRecommendationsViewController.swift:0 [opt]
frame #11: 0x00000001001fde24 MyApp`_TPA__TTSg5C8MyApp18AddressBookContact_T____TFFSa42_withUnsafeMutableBufferPointerIfSupportedu__rFRGSaq__FzFzTGVSs20UnsafeMutablePointerq__Si_qd__GSqqd___U_FzRGVSs26UnsafeMutableBufferPointerQd___Q_ [inlined] generic specialization <MyApp.AddressBookContact, ()> of Swift.Array.(_withUnsafeMutableBufferPointerIfSupported <A><B> (inout Swift.Array<A>) -> ((Swift.UnsafeMutablePointer<A>, Swift.Int) throws -> B) throws -> Swift.Optional<B>).(closure #1) + 36 at RequestRecommendationsViewController.swift:0 [opt]
frame #12: 0x00000001001fde00 MyApp`_TPA__TTSg5C8MyApp18AddressBookContact_T____TFFSa42_withUnsafeMutableBufferPointerIfSupportedu__rFRGSaq__FzFzTGVSs20UnsafeMutablePointerq__Si_qd__GSqqd___U_FzRGVSs26UnsafeMutableBufferPointerQd___Q_ + 52 at RequestRecommendationsViewController.swift:0 [opt]
frame #13: 0x00000001002026e8 MyApp`generic specialization <MyApp.AddressBookContact, ()> of Swift.Array.withUnsafeMutableBufferPointer <A><B> (inout Swift.Array<A>)((inout Swift.UnsafeMutableBufferPointer<A>) throws -> B) throws -> B + 320 at RequestRecommendationsViewController.swift:0 [opt]
frame #14: 0x0000000100203134 MyApp`function signature specialization <Arg[0] = Owned To Guaranteed> of generic specialization <Swift.Array<MyApp.AddressBookContact> with Swift.Array<MyApp.AddressBookContact> : Swift.MutableCollectionType in Swift, Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.Array<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.RandomAccessIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int with Swift.Int : Swift.SignedNumberType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact> with Swift.ArraySlice<MyApp.AddressBookContact> : Swift.Indexable in Swift and Swift.ArraySlice<MyApp.AddressBookContact> : Swift.SequenceType in Swift, Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> with Swift.IndexingGenerator<Swift.ArraySlice<MyApp.AddressBookContact>> : Swift.GeneratorType in Swift, MyApp.AddressBookContact, Swift.Int with Swift.Int : Swift.ForwardIndexType in Swift, Swift.Int with Swift.Int : Swift._SignedIntegerType in Swift, Swift.Int with Swift.Int : Swift._BuiltinIntegerLiteralConvertible in Swift, Swift.Int, Swift.ArraySlice<MyApp.AddressBookContact>, MyApp.AddressBookContact, MyApp.AddressBookContact> of ext.Swift.Swift.MutableCollectionType<A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType>.sortInPlace <A where A: Swift.MutableCollectionType, A.Index: Swift.RandomAccessIndexType> (inout A)((A.Generator.Element, A.Generator.Element) -> Swift.Bool) -> () + 204 at RequestRecommendationsViewController.swift:0 [opt]
frame #15: 0x00000001001fe568 MyApp`MyApp.RequestRecommendationsViewController.(contacts=(null) at x27, error=<unavailable>, self=<unavailable>) (MyApp.RequestRecommendationsViewController) -> () -> ()).(closure #2) + 1444 at RequestRecommendationsViewController.swift:112 [opt]
frame #16: 0x0000000102469ca8 libdispatch.dylib`_dispatch_call_block_and_release + 24
frame #17: 0x0000000102469c68 libdispatch.dylib`_dispatch_client_callout + 16
frame #18: 0x000000010246f710 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 2096
frame #19: 0x00000001853001f8 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
frame #20: 0x00000001852fe060 CoreFoundation`__CFRunLoopRun + 1628
frame #21: 0x000000018522cca0 CoreFoundation`CFRunLoopRunSpecific + 384
frame #22: 0x0000000190468088 GraphicsServices`GSEventRunModal + 180
frame #23: 0x000000018a944ffc UIKit`UIApplicationMain + 204
frame #24: 0x00000001001bc838 MyApp`main + 144 at AppDelegate.swift:22 [opt]
frame #25: 0x000000019a74a8b8 libdyld.dylib`start + 4