(gdb) bt
#0  0x000055555582d049 in zend_std_cast_object_tostring (readobj=0x7fffea527ed0, writeobj=0x7fffff7ff080, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#1  0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527ed0) at ./Zend/zend_operators.c:878
#2  0x0000555555868028 in zval_get_string (op=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:37346
#3  ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#4  0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#5  0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff7ff270, fci_cache=<optimized out>, fci_cache@entry=0x7fffff7ff250) at ./Zend/zend_execute_API.c:756
#6  0x0000555555817a3d in zend_call_method (object=0x7fffea527da0, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff7ff340, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#7  0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff7ff3c0, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#8  0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527da0) at ./Zend/zend_operators.c:878
#9  0x0000555555868028 in zval_get_string (op=0x7fffea527da0) at ./Zend/zend_vm_execute.h:37346
#10 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#11 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#12 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff7ff5b0, fci_cache=<optimized out>, fci_cache@entry=0x7fffff7ff590) at ./Zend/zend_execute_API.c:756
#13 0x0000555555817a3d in zend_call_method (object=0x7fffea527c70, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff7ff680, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#14 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff7ff700, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#15 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527c70) at ./Zend/zend_operators.c:878
#16 0x0000555555868028 in zval_get_string (op=0x7fffea527c70) at ./Zend/zend_vm_execute.h:37346
#17 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#18 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#19 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff7ff8f0, fci_cache=<optimized out>, fci_cache@entry=0x7fffff7ff8d0) at ./Zend/zend_execute_API.c:756
#20 0x0000555555817a3d in zend_call_method (object=0x7fffea527b40, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff7ff9c0, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#21 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff7ffa40, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#22 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527b40) at ./Zend/zend_operators.c:878
#23 0x0000555555868028 in zval_get_string (op=0x7fffea527b40) at ./Zend/zend_vm_execute.h:37346
#24 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#25 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#26 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff7ffc30, fci_cache=<optimized out>, fci_cache@entry=0x7fffff7ffc10) at ./Zend/zend_execute_API.c:756
#27 0x0000555555817a3d in zend_call_method (object=0x7fffea527a10, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff7ffd00, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#28 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff7ffd80, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#29 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527a10) at ./Zend/zend_operators.c:878
#30 0x0000555555868028 in zval_get_string (op=0x7fffea527a10) at ./Zend/zend_vm_execute.h:37346
#31 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#32 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#33 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff7fff70, fci_cache=<optimized out>, fci_cache@entry=0x7fffff7fff50) at ./Zend/zend_execute_API.c:756
#34 0x0000555555817a3d in zend_call_method (object=0x7fffea5278e0, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff800040, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#35 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff8000c0, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#36 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea5278e0) at ./Zend/zend_operators.c:878
#37 0x0000555555868028 in zval_get_string (op=0x7fffea5278e0) at ./Zend/zend_vm_execute.h:37346
#38 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#39 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#40 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff8002b0, fci_cache=<optimized out>, fci_cache@entry=0x7fffff800290) at ./Zend/zend_execute_API.c:756
#41 0x0000555555817a3d in zend_call_method (object=0x7fffea5277b0, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff800380, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#42 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff800400, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#43 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea5277b0) at ./Zend/zend_operators.c:878
#44 0x0000555555868028 in zval_get_string (op=0x7fffea5277b0) at ./Zend/zend_vm_execute.h:37346
#45 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#46 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#47 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff8005f0, fci_cache=<optimized out>, fci_cache@entry=0x7fffff8005d0) at ./Zend/zend_execute_API.c:756
#48 0x0000555555817a3d in zend_call_method (object=0x7fffea527680, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff8006c0, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#49 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff800740, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703
#50 0x00005555557f36da in zval_get_string_func (op=op@entry=0x7fffea527680) at ./Zend/zend_operators.c:878
#51 0x0000555555868028 in zval_get_string (op=0x7fffea527680) at ./Zend/zend_vm_execute.h:37346
#52 ZEND_CAST_SPEC_CV_HANDLER () at ./Zend/zend_vm_execute.h:37342
#53 0x000055555587b4d5 in execute_ex (ex=0x7fffea527ed0) at ./Zend/zend_vm_execute.h:59313
#54 0x00005555557edd4e in zend_call_function (fci=fci@entry=0x7fffff800930, fci_cache=<optimized out>, fci_cache@entry=0x7fffff800910) at ./Zend/zend_execute_API.c:756
#55 0x0000555555817a3d in zend_call_method (object=0x7fffea527550, obj_ce=<optimized out>, obj_ce@entry=0x7fffea869400, fn_proxy=fn_proxy@entry=0x7fffea869530, function_name=function_name@entry=0x5555558dd1b4 "__tostring",
    function_name_len=function_name_len@entry=10, retval_ptr=retval_ptr@entry=0x7fffff800a00, param_count=0, arg1=0x0, arg2=0x0) at ./Zend/zend_interfaces.c:103
#56 0x000055555582d061 in zend_std_cast_object_tostring (readobj=<optimized out>, writeobj=0x7fffff800a80, type=<optimized out>) at ./Zend/zend_object_handlers.c:1703