bug: `set_linearization!()` does not work as intended

[giannipetrella]

Currently the following code errors.

julia> Q, d, theta = kronecker_quiver(3), [2, 3], [3, -2];

julia> M = QuiverModuliSpace(Q, d, theta);

julia> QuiverTools.set_linearization!(M, [-1, 1]);

julia> U1 = universal_bundle(M, 1)
ERROR: UndefRefError: access to undefined reference
Stacktrace:
 [1] getproperty
   @ ./Base.jl:49 [inlined]
 [2] chow_ring(M::QuiverModuliSpace; chi::UndefInitializer)
   @ QuiverTools ~/.julia/packages/QuiverTools/W5Eci/src/Chow.jl:267
 [3] chow_ring
   @ ~/.julia/packages/QuiverTools/W5Eci/src/Chow.jl:236 [inlined]
 [4] total_chern_class_universal(M::QuiverModuliSpace, i::Int64)
   @ QuiverTools ~/.julia/packages/QuiverTools/W5Eci/src/Chow.jl:435
 [5] universal_bundle(M::QuiverModuliSpace, i::Int64)
   @ QuiverTools ~/.julia/packages/QuiverTools/W5Eci/src/Bundles.jl:711
 [6] top-level scope
   @ REPL[6]:1

This must be an issue with the way the linearisation is set in the ChowRing container and accessed by the constructor.
Trying to set a new Chow ring with chow_ring(M) or chow_ring(M; chi=[-1, 1]) does not work either, presumably for the same reason.

[pbelmans]

What's the precise error?

[giannipetrella]

Updated the code with exact terminal output. It has to do with how linearisations are initialised (as nothing) and updated I believe.