fix: fix defaulting allow_algebraic = fully_determined

Author: AayushSabharwal

src/systems/systems.jl

@@ -25,21 +25,21 @@ topological sort of the observed equations in `sys`.
 ### Optional Keyword Arguments:
 + When `simplify=true`, the `simplify` function will be applied during the tearing
   process.
-+ `allow_symbolic=false`, `allow_algebraic=nothing`, `allow_parameter=true`, and
++ `allow_symbolic=false`, `allow_algebraic=fully_determined`, `allow_parameter=true`, and
   `conservative=false` limit the coefficient types during tearing. In particular,
   `conservative=true` limits tearing to only solve for trivial linear systems where
   the coefficient has the absolute value of ``1``. `allow_symbolic` allows arbitrary
   symbolic coefficients. If it is false, `allow_algebraic` allows symbolic coefficients
   involving only algebraic variables and parameters. Otherwise, `allow_parameter` only
   allows coefficients containing parameters. `allow_algebraic` defaults to
-  `fully_determined` if `nothing`.
+  `fully_determined`.
 + `fully_determined=true` controls whether or not an error will be thrown if the number
   of equations don't match the number of inputs, outputs, and equations.
 """
 function structural_simplify(
         sys::AbstractSystem, io = nothing; additional_passes = [], simplify = false, split = true,
-        allow_symbolic = false, allow_algebraic = nothing, allow_parameter = true, conservative = false,
-        fully_determined = true, kwargs...)
+        fully_determined = true, allow_symbolic = false, allow_algebraic = fully_determined,
+        allow_parameter = true, conservative = false, kwargs...)
     isscheduled(sys) && throw(RepeatedStructuralSimplificationError())
     newsys′ = __structural_simplify(sys, io; simplify, allow_symbolic, allow_algebraic,
         allow_parameter, conservative, fully_determined, kwargs...)