Missing `parameter_values` for MTKParameters/param structure

[aml5600]

Describe the bug 🐞

From slack thread here.

Expected behavior

MTKParameters is returned itself.

Minimal Reproducible Example 👇

Without MRE, we would only be able to help you to a limited extent, and attention to the issue would be limited. to know more about MRE refer to wikipedia and stackoverflow.

 @mtkmodel Simple begin
    @parameters begin
        a = 1.0
        b = 1.0
    end
    @variables begin
        x(t)
    end
    @equations begin
        D(x) ~ -a * x + b
    end
end
@named model = Simple()
model = complete(model)

p = MTKParameters(model, defaults(model))
setter = ModelingToolkit.setp_oop(model, [model.a])

function loss(x)
    new_p = setter(p, [x])
    # do something with new_p and the model...
    return sum(abs2, new_p.tunable) # for example
end

Error & Stacktrace ⚠️

MethodError: no method matching parameter_values(::MTKParameters{Vector{Float64}, Tuple{}, Tuple{}, Tuple{}, Tuple{}})

[aml5600]

FYI @AayushSabharwal