Make 'docs' optional

src/librustdoc/json/conversions.rs

@@ -27,7 +27,7 @@ impl JsonRenderer<'_> {
                 name: name.map(|sym| sym.to_string()),
                 source: self.convert_span(source),
                 visibility: self.convert_visibility(visibility),
-                docs: attrs.collapsed_doc_value().unwrap_or_default(),
+                docs: attrs.collapsed_doc_value(),
                 links: attrs
                     .links
                     .into_iter()

src/librustdoc/json/types.rs

@@ -69,7 +69,7 @@ pub struct Item {
     /// so this field is needed to differentiate.
     pub visibility: Visibility,
     /// The full markdown docstring of this item.
-    pub docs: String,
+    pub docs: Option<String>,
     /// This mapping resolves [intra-doc links](https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md) from the docstring to their IDs
     pub links: FxHashMap<String, Id>,
     /// Stringified versions of the attributes on this item (e.g. `"#[inline]"`)