Merge pull request #4041 from SciML/as/fix-hybrid

fix: minor fixes for clock stuff

Author: AayushSabharwal

src/discretedomain.jl

@@ -209,6 +209,7 @@ end
 is_transparent_operator(::Type{Hold}) = true
 
 (D::Hold)(x) = Term{symtype(x)}(D, Any[x])
+(D::Hold)(x::Number) = x
 (D::Hold)(x::Num) = Num(D(value(x)))
 SymbolicUtils.promote_symtype(::Hold, x) = x
 Base.nameof(::Hold) = :Hold

src/systems/abstractsystem.jl

@@ -2796,7 +2796,7 @@ function process_parameter_equations(sys::AbstractSystem)
     eqs = equations(sys)
     for (i, eq) in enumerate(eqs)
         empty!(varsbuf)
-        vars!(varsbuf, eq; op = Union{Differential, Initial, Pre})
+        vars!(varsbuf, eq; op = Union{Differential, Initial, Pre, Hold, Sample})
         # singular equations
         isempty(varsbuf) && continue
         if all(varsbuf) do sym