Add support for not nil ref types

json_serialization/reader.nim

@@ -1,3 +1,5 @@
+{.experimental: "notnil".}
+
 import
   strutils, typetraits, macros, strformat,
   faststreams/input_stream, serialization/[object_serialization, errors],
@@ -164,6 +166,9 @@ func maxAbsValue(T: type[SomeInteger]): uint64 {.compileTime.} =
   elif T is int64: 9223372036854775808'u64
   else: uint64(high(T))
 
+proc isNotNilCheck[T](x: ref T not nil) {.compileTime.} = discard
+proc isNotNilCheck[T](x: ptr T not nil) {.compileTime.} = discard
+
 proc readValue*(r: var JsonReader, value: var auto) =
   mixin readValue
 
@@ -182,6 +187,10 @@ proc readValue*(r: var JsonReader, value: var auto) =
     r.lexer.next()
 
   elif value is ref|ptr:
+    when compiles(isNotNilCheck(value)):
+      allocPtr value
+      value[] = readValue(r, type(value[]))
+    else:
       if tok == tkNull:
         value = nil
         r.lexer.next()