Punctuation per style guide

Author: handrews

src/oas.md

@@ -3469,8 +3469,8 @@ XML does not, by default, have a concept equivalent to `null`, and to preserve c
 
 However, implementations SHOULD handle `null` values as follows:
 
-* For elements, produce an empty element with an `xsi:nil="true"` attribute
-* For attributes, omit the attribute
+* For elements, produce an empty element with an `xsi:nil="true"` attribute.
+* For attributes, omit the attribute.
 
 Note that for attributes, this makes either a `null` value or a missing property serialize to an omitted attribute.
 As the Schema Object validates the in-memory representation, this allows handling the combination of `null` and a required property.