fix: fix generate_initializesystem(::JumpSystem)

Author: AayushSabharwal

src/systems/nonlinear/initializesystem.jl

@@ -13,7 +13,9 @@ function generate_initializesystem(sys::AbstractSystem;
         check_units = true, check_defguess = false,
         name = nameof(sys), extra_metadata = (;), kwargs...)
     eqs = equations(sys)
-    eqs = filter(x -> x isa Equation, eqs)
+    if !(eqs isa Vector{Equation})
+        eqs = Equation[x for x in eqs if x isa Equation]
+    end
     trueobs, eqs = unhack_observed(observed(sys), eqs)
     vars = unique([unknowns(sys); getfield.(trueobs, :lhs)])
     vars_set = Set(vars) # for efficient in-lookup