Do not emit (Preserve | Preserve) types

src/preserves/private/preserves_schema_nim.nim

@@ -345,13 +345,18 @@ proc generateProcs(result: var seq[PNode]; name: string; sn: SchemaNode) =
         sn.nodes[0].toNimLit)
     for i, field in sn.nodes:
       if i > 0:
-        let id = field.ident
+        let
+          id = field.ident
+        var fieldType  = field.typeIdent
+        if fieldType.kind != nkIdent or fieldType.ident.s != "Preserve":
+          fieldType =
+            nn(nkInfix,
+              ident"|",
+              fieldType,
+              ident"Preserve")
         params.add nn(nkIdentDefs,
           id,
-          nn(nkInfix,
-            ident"|",
-            ident"Preserve",
-            field.typeIdent),
+          fieldType,
           newEmpty())
         initRecordCall.add(
           nn(nkCall, ident"toPreserve", id, ident"EmbeddedType"))