remove conflicting default impl

src/parser.rs

@@ -50,6 +50,7 @@ impl ConfigField {
                             derive.contains("Tree")
                                 || derive.contains("Serialize")
                                 || derive.contains("Deserialize")
+                                || (self.default.is_some() && derive.contains("Default"))
                         }) == Some(false)
                     });
                     quote! {#[derive(#(#derives,)*)]}