how to support null species as reactant or product in a reaction?

how to add a nullspecies in a reaction as a reactant or product ? i am trying along following lines

using GillesPy2
dnadimer_repressor = GillesPy2.model()
k1 = GillesPy2.parameter("k1", .09)
k2 = GillesPy2.parameter("k2", .05)
k3 = GillesPy2.parameter("k3", .001)
k4 = GillesPy2.parameter("k4", .0009)
k5 = GillesPy2.parameter("k5", .00001)
k6 = GillesPy2.parameter("k6", .0005)
k7 = GillesPy2.parameter("k7", .005)
k8 = GillesPy2.parameter("k8", 0.1)
dnadimer_repressor.add_parameter([k1, k2, k3, k4, k5, k6, k7, k8])
G = GillesPy2.species("G", 1000)
M = GillesPy2.species("M", 0)
P = GillesPy2.species("P", 0)
P2 = GillesPy2.species("P2", 0)
P2G = GillesPy2.species("P2G", 0)
null = GillesPy2.species("null", 0)
dnadimer_repressor.add_species([G, M, P, P2, P2G, null])
r1 = GillesPy2.reaction("k1", Dict(G => 1), Dict(G => 1, M => 1), k1)
r2 = GillesPy2.reaction("k2", Dict(M => 1), Dict(M => 1, P => 1), k2)
r3 = GillesPy2.reaction("k3", Dict(M => 1), Dict(null => 0), k3)
r4 = GillesPy2.reaction("k4", Dict(P => 1), Dict(null => 0), k4)
r5 = GillesPy2.reaction("k5", Dict(P => 2), Dict(P2 => 1), k5)
r6 = GillesPy2.reaction("k6", Dict(P2 => 1), Dict(P => 2), k6)
r7 = GillesPy2.reaction("k7", Dict(P2 => 1, G => 1), Dict(P2G => 1), k7)
r8 = GillesPy2.reaction("k8", Dict(P2G => 1), Dict(P2 => 1, G => 1), k8)
dnadimer_repressor.add_reaction([r1, r2, r3, r4, r5, r6, r7, r8])

this results in a error as follows

ERROR: PyError ($(Expr(:escape, :(ccall(#= /home/chetan/.julia/packages/PyCall/BD546/src/pyfncall.jl:43 =# @pysym(:PyObject_Call), PyPtr, (PyPtr, PyPtr, PyPtr), o, pyargsptr, kw))))) <class 'gillespy2.core.gillespyError.ParameterError'>
ParameterError('Error using k1\n\tReactants\n\t\tG: 1\n\tProducts\n\t\tG: 1\n\t\tM: 1\n\tPropensity Function: k1*G as a Reaction. Reason given: Name "k1" is unavailable. A parameter with that name exists.')
  File "/home/chetan/.local/lib/python3.8/site-packages/gillespy2/core/model.py", line 500, in add_reaction
    self.add_reaction(r)
  File "/home/chetan/.local/lib/python3.8/site-packages/gillespy2/core/model.py", line 530, in add_reaction
    raise ParameterError("Error using {} as a Reaction. Reason given: {}".format(reactions, e))

Stacktrace:
  [1] pyerr_check
    @ ~/.julia/packages/PyCall/BD546/src/exception.jl:62 [inlined]
  [2] pyerr_check
    @ ~/.julia/packages/PyCall/BD546/src/exception.jl:66 [inlined]
  [3] _handle_error(msg::String)
    @ PyCall ~/.julia/packages/PyCall/BD546/src/exception.jl:83
  [4] macro expansion
    @ ~/.julia/packages/PyCall/BD546/src/exception.jl:97 [inlined]
  [5] #107
    @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:43 [inlined]
  [6] disable_sigint
    @ ./c.jl:458 [inlined]
  [7] __pycall!
    @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:42 [inlined]
  [8] _pycall!(ret::PyCall.PyObject, o::PyCall.PyObject, args::Tuple{Vector{PyCall.PyObject}}, nargs::Int64, kw::Ptr{Nothing})
    @ PyCall ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:29
  [9] _pycall!
    @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:11 [inlined]
 [10] #_#114
    @ ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:86 [inlined]
 [11] (::PyCall.PyObject)(args::Vector{PyCall.PyObject})
    @ PyCall ~/.julia/packages/PyCall/BD546/src/pyfncall.jl:86
 [12] top-level scope
    @ none:1

StochSS / GillesPy2lia

how to support null species as reactant or product in a reaction? #1