For struct with `nothing` as default value, `find` converts non-NULL fields in the DB record to `nothing`

Full code for the MWE here: https://github.com/GenieFramework/CodeExamples/tree/main/src/3.database/null_values

I have a struct where one of its fields can be `Int`or `Nothing`

```julia
@kwdef mutable struct House <: AbstractModel
id::DbId = DbId()
street::String = "Random street"
size::Float32 = 100.0
rooms::Union{Int64,Nothing,Missing} = nothing
end
```

When running this to load two hoses, one with `nothing`in rooms and oner with `4`
```julia
using SearchLight
using SearchLightSQLite
include("app/resources/houses/Houses.jl")
using .Houses
# Base.convert(t::Type{Nothing}, x::Int64) = x

SearchLight.Configuration.load() |> SearchLight.connect

h = House(street="Barcelona 2", size=400, rooms=nothing)
save(h)
h = House(street="Barcelona 3", size=400, rooms=4)
save(h)

@show find(House, SQLWhereExpression("street ==? AND size == ?", "Barcelona 2", 400))
@show find(House, SQLWhereExpression("street ==? AND size == ?", "Barcelona 3", 400))

```
the first one works, but the second one errors:

```julia
[ Info: SELECT "houses"."id" AS "houses_id", "houses"."street" AS "houses_street", "houses"."size" AS "houses_size", "houses"."rooms" AS "houses_
rooms" FROM "houses" WHERE street =='Barcelona 2' AND size == 400 ORDER BY houses.id ASC
find(House, SQLWhereExpression("street ==? AND size == ?", "Barcelona 2", 400)) = House[House
| KEY | VALUE |
|----------------|-------------|
| id::DbId | 2 |
| rooms::Nothing | nothing |
| size::Float32 | 400.0 |
| street::String | Barcelona 2 |
]
[ Info: SELECT "houses"."id" AS "houses_id", "houses"."street" AS "houses_street", "houses"."size" AS "houses_size", "houses"."rooms" AS "houses_
rooms" FROM "houses" WHERE street =='Barcelona 3' AND size == 400 ORDER BY houses.id ASC
┌ Error: MethodError(convert, (Nothing, 4), 0xffffffffffffffff)
└ @ SearchLight ~/.julia/packages/SearchLight/Ps2Js/src/SearchLight.jl:543
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Nothing
**Error stacktrace**
```

It appears that `find`converts the field in the record to the type of the **default value in the struct**. One would expect it to convert to the other type in the Union when the record value is non-NULL.

I've done a quickfix by extending `convert` to return the record value when it is not NULL.

```julia
Base.convert(t::Type{Nothing}, x::Int64) = x
```