don't use experimental (in 1.36) Self:: access for enums

Author: kvnvelasco

src/value/from.rs

@@ -275,7 +275,7 @@ where
 {
     fn from(opt: Option<T>) -> Self {
         match opt {
-            None => Self::Null,
+            None => Value::Null,
             Some(value) => Into::into(value),
         }
     }