ZXGraphlikeOptimisation() can cause RunTime error

[IlanIwumbwe]

Benny and I found this by generating a random Pytket circuit.

When we run this code:

from pytket import Circuit
from pytket.passes import ZXGraphlikeOptimisation

main_circ = Circuit(6, 0, "main_circ")

# Applying gates 
main_circ.Rx(-0.78,3)
main_circ.Rx(1.069,5)
main_circ.CX(0, 3)
main_circ.CX(3, 5)
main_circ.CX(0, 5)
main_circ.Rx(1.069,3)
main_circ.Rx(-5.958,4)
main_circ.CX(3, 4)
main_circ.CX(3, 5)
main_circ.CX(0, 3)

ZXGraphlikeOptimisation().apply(main_circ)

We get this runtime error:

RuntimeError: Error during extraction from ZX diagram: diagram does not have gflow

We tried to minimize the test case but deleting any one of the gates would make it work. Additionally, if any of the arguments to the rotation gates are integers, it also works.

[cqc-alec]

Any ideas @willsimmons1465 ? Seems like ZXGraphlikeOptimisation should be applicable to this circuit?