feat: do not unwrap() potentially None references.

feat: add new `Error` variant `NoReference`

Author: bitfl0wer

crates/oas3/src/spec/media_type.rs

@@ -33,7 +33,9 @@ impl MediaType {
     pub fn schema(&self, spec: &Spec) -> Result<ObjectSchema, Error> {
         self.schema
             .as_ref()
-            .unwrap()
+            .ok_or(Error::Ref(super::RefError::NoReference(
+                super::RefType::Schema,
+            )))?
             .resolve(spec)
             .map_err(Error::Ref)
     }

crates/oas3/src/spec/operation.rs

@@ -132,7 +132,9 @@ impl Operation {
     pub fn request_body(&self, spec: &Spec) -> Result<RequestBody, Error> {
         self.request_body
             .as_ref()
-            .unwrap()
+            .ok_or(Error::Ref(super::RefError::NoReference(
+                super::RefType::RequestBody,
+            )))?
             .resolve(spec)
             .map_err(Error::Ref)
     }

crates/oas3/src/spec/ref.rs

@@ -54,6 +54,10 @@ pub enum RefError {
     /// Reference path points outside the given spec file.
     #[display("Unresolvable path: {}", _0)]
     Unresolvable(#[error(not(source))] String), // TODO: use some kind of path structure
+
+    /// `Option<ObjectOrReference<_>>` evaluated to be `None`.
+    #[display("Cannot attempt to resolve this reference because Option<ObjectOrReference<{}>> evaluated to None", _0)]
+    NoReference(#[error(not(source))] RefType),
 }
 
 /// Component type of a reference.