fixup! fix: fix nothing default overrides being ignored

Author: AayushSabharwal

src/systems/diffeqs/odesystem.jl

@@ -241,7 +241,8 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
     var_to_name = Dict()
     process_variables!(var_to_name, defaults, dvs′)
     process_variables!(var_to_name, defaults, ps′)
-    defaults = Dict{Any, Any}(value(k) => value(v) for (k, v) in pairs(defaults))
+    defaults = Dict{Any, Any}(value(k) => value(v)
+    for (k, v) in pairs(defaults) if v !== nothing)
 
     sysdvsguesses = [ModelingToolkit.getguess(st) for st in dvs′]
     hasaguess = findall(!isnothing, sysdvsguesses)