Some fixes to nullability (#365)

ConsumePlugin/GeneratedJson.fs

@@ -71,6 +71,7 @@ module JsonRecordType =
                  )
              | v -> v)
                 .AsArray ()
+            |> Seq.cast<System.Text.Json.Nodes.JsonNode>
             |> Seq.map (fun elt -> elt.AsValue().GetValue<System.Int32> ())
             |> Array.ofSeq
 
@@ -84,6 +85,7 @@ module JsonRecordType =
                  )
              | v -> v)
                 .AsArray ()
+            |> Seq.cast<System.Text.Json.Nodes.JsonNode>
             |> Seq.map (fun elt -> elt.AsValue().GetValue<System.String> ())
             |> Array.ofSeq
 
@@ -109,6 +111,7 @@ module JsonRecordType =
                  )
              | v -> v)
                 .AsArray ()
+            |> Seq.cast<System.Text.Json.Nodes.JsonNode>
             |> Seq.map (fun elt -> elt.AsValue().GetValue<System.Int32> ())
             |> List.ofSeq
 
@@ -201,7 +204,15 @@ module ToGetExtensionMethodJsonParseExtension =
 
         /// Parse from a JSON node.
         static member jsonParse (node : System.Text.Json.Nodes.JsonNode) : ToGetExtensionMethod =
-            let arg_20 = System.Numerics.BigInteger.Parse (node.["whiskey"].ToJsonString ())
+            let arg_20 =
+                let v = node.["whiskey"]
+
+                System.Numerics.BigInteger.Parse (
+                    (match v with
+                     | null -> raise (System.ArgumentNullException ())
+                     | v -> v)
+                        .ToJsonString ()
+                )
 
             let arg_19 =
                 (match node.["victor"] with