Marlin will not compile error: 'MYSERIAL' was not declared in this scope

[kknox9713]

I'm trying to compile Marlin 2.0 for my skr mini 3 and I keep getting the following.
In file included from Marlin\src\HAL\shared\backtrace\backtrace.cpp:28:0:
Marlin\src\HAL\shared\backtrace\backtrace.cpp: In function 'bool UnwReportOut(void*, const UnwReport*)':
Marlin\src\HAL\shared\backtrace../../../core/serial.h:68:40: error: 'MYSERIAL' was not declared in this scope
#define SERIAL_OUT(WHAT, V...) (void)MYSERIAL.WHAT(V)
^
Marlin\src\HAL\shared\backtrace../../../core/serial.h:94:27: note: in expansion of macro 'SERIAL_OUT'
#define _CHAR_1(c) SERIAL_OUT(write, c)
^~~~~~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:92:27: note: in expansion of macro '_CHAR_1'
#define __CHAR_N(N,V...) CHAR##N(V)
Compiling .pio\build\STM32F103RC_btt_512K\src\src\HAL\shared\backtrace\unwmemaccess.cpp.o
^~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:93:27: note: in expansion of macro '__CHAR_N'
#define _CHAR_N(N,V...) __CHAR_N(N,V)
^~~~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:105:27: note: in expansion of macro '_CHAR_N'
#define SERIAL_CHAR(V...) _CHAR_N(NUM_ARGS(V),V)
^~~~~~~
Marlin\src\HAL\shared\backtrace\backtrace.cpp:37:3: note: in expansion of macro 'SERIAL_CHAR'
SERIAL_CHAR('#'); SERIAL_PRINT(*p, DEC); SERIAL_ECHOPGM(" : ");
^~~~~~~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:68:40: note: suggested alternative: 'MSERIAL'
#define SERIAL_OUT(WHAT, V...) (void)MYSERIAL.WHAT(V)
^
Marlin\src\HAL\shared\backtrace../../../core/serial.h:94:27: note: in expansion of macro 'SERIAL_OUT'
#define _CHAR_1(c) SERIAL_OUT(write, c)
^~~~~~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:92:27: note: in expansion of macro '_CHAR_1'
#define __CHAR_N(N,V...) CHAR##N(V)
^~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:93:27: note: in expansion of macro '__CHAR_N'
#define _CHAR_N(N,V...) __CHAR_N(N,V)
^~~~~~~~
Marlin\src\HAL\shared\backtrace../../../core/serial.h:105:27: note: in expansion of macro '_CHAR_N'
#define SERIAL_CHAR(V...) _CHAR_N(NUM_ARGS(V),V)
^~~~~~~
Marlin\src\HAL\shared\backtrace\backtrace.cpp:37:3: note: in expansion of macro 'SERIAL_CHAR'
SERIAL_CHAR('#'); SERIAL_PRINT(*p, DEC); SERIAL_ECHOPGM(" : ");
^~~~~~~~~~~
*** [.pio\build\STM32F103RC_btt_512K\src\src\HAL\shared\backtrace\backtrace.cpp.o] Error 1