macros + sqlite: fix error for null-typed columns

sqlx-core/src/sqlite/types/mod.rs

@@ -66,6 +66,10 @@ impl TypeInfo for SqliteTypeInfo {
     fn compatible(&self, other: &Self) -> bool {
         self.affinity == other.affinity
     }
+
+    fn is_null_type(&self) -> bool {
+        self.r#type == SqliteType::Null
+    }
 }
 
 impl<'de, T> Decode<'de, Sqlite> for Option<T>