From 6894f28de201c2d0188b73d24e7e43a8b2a4340e Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <51025924+simsurace@users.noreply.github.com>
Date: Mon, 5 Feb 2024 20:45:44 +0100
Subject: [PATCH] Add support for `nothing`

I have been using this quite often to conditionally drop specific parameters.
---
 src/flatten.jl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/flatten.jl b/src/flatten.jl
index 82d5b60..ce68646 100644
--- a/src/flatten.jl
+++ b/src/flatten.jl
@@ -19,6 +19,12 @@ function flatten end
 
 flatten(x) = flatten(Float64, x)
 
+function ParameterHandling.flatten(::Type{T}, ::Nothing) where {T<:Real} 
+    v = T[]
+    unflatten_to_Nothing(::Vector{T}) = nothing
+    return v, unflatten_to_Nothing
+end
+
 function flatten(::Type{T}, x::Integer) where {T<:Real}
     v = T[]
     unflatten_to_Integer(v::Vector{T}) = x