#0  operator-> (this=0xffffffff) at ../Source/JavaScriptCore/runtime/WriteBarrier.h:123
  [Error: WriteBarrier.h was not found in source tree]
#1  isString (this=0xffffffff) at ../Source/JavaScriptCore/runtime/JSCellInlines.h:124
  [Error: JSCellInlines.h was not found in source tree]
#2  JSC::JSCell::toPrimitive (this=0xffffffff, exec=exec@entry=0x7f6567b7fb58, preferredType=preferredType@entry=JSC::PreferString) at ../Source/JavaScriptCore/runtime/JSCell.cpp:128
  [Error: JSCell.cpp was not found in source tree]
#3  0x00007f65d721a33b in JSC::JSValue::toStringSlowCase (this=<optimized out>, exec=0x7f6567b7fb58) at ../Source/JavaScriptCore/runtime/JSCJSValue.cpp:312
  [Error: JSCJSValue.cpp was not found in source tree]
#4  0x00007f65d7085d65 in JSC::getByVal (exec=0x7f6567b7fb58, baseValue=..., subscript=..., returnAddress=...) at ../Source/JavaScriptCore/jit/JITOperations.cpp:1383
  [Error: JITOperations.cpp was not found in source tree]
#5  0x00007f65d7086242 in JSC::operationGetByValGeneric (exec=<optimized out>, encodedBase=<optimized out>, encodedSubscript=<optimized out>) at ../Source/JavaScriptCore/jit/JITOperations.cpp:1396
  [Error: JITOperations.cpp was not found in source tree]
#6  0x00007f656cd7ea5e in ?? ()
#7  0x0000000000000000 in ?? ()