fix(utoipa-gen): degenerate oneOf when using Option<_> + nullable = false + default

Author: Jean-Marc Le Roux

utoipa-gen/src/component.rs

@@ -1358,7 +1358,7 @@ impl ComponentSchema {
                         // TODO: refs support `summary` field but currently there is no such field
                         // on schemas more over there is no way to distinct the `summary` from
                         // `description` of the ref. Should we consider supporting the summary?
-                        let schema = if default.is_some() || nullable || title.is_some() {
+                        let schema = if nullable {
                             composed_or_ref(quote_spanned! {type_path.span()=>
                                 utoipa::openapi::schema::OneOfBuilder::new()
                                     #nullable_item
@@ -1374,6 +1374,7 @@ impl ComponentSchema {
                                 utoipa::openapi::schema::RefBuilder::new()
                                     #description_stream
                                     .ref_location_from_schema_name(#name_tokens)
+                                    #default_tokens
                             })
                         };