Program refuses to compile

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After further investigation I found out that the program does compile if I remove the SAVE command so this is a regression bug but it still bombs if I try to compile it with -O3 with this message, I had to stop the compiler from running by hitting Ctrl-C.

Traceback (most recent call last):
File "/home/pi/zxbasic/zxb.py", line 348, in <module>
sys.exit(main(sys.argv)) # Exit
File "/home/pi/zxbasic/zxb.py", line 301, in main
asm_output = optimize(asm_output) + '\n'
File "/home/pi/zxbasic/optimizer.py", line 2296, in optimize
x.optimize()
File "/home/pi/zxbasic/optimizer.py", line 1948, in optimize
regs.op(i1, o1)
File "/home/pi/zxbasic/optimizer.py", line 869, in op
self.set('a', 0xFF ^ self.getv('a'))
TypeError: unsupported operand type(s) for ^: 'int' and 'NoneType'

Something strange going on here.