fix: allow $ref pointers to point to a null value

Author: erunion

lib/pointer.ts

@@ -121,6 +121,14 @@ class Pointer<S extends object = JSONSchema, O extends ParserOptions<S> = Parser
           continue;
         }
 
+        // If the token we're looking for ended up not containing any slashes but is
+        // actually instead pointing to an existing `null` value then we should use that
+        // `null` value.
+        if (token in this.value && this.value[token] === null) {
+          this.value = null;
+          continue;
+        }
+
         this.value = null;
 
         const path = this.$ref.path || "";

test/specs/dereference-null-ref/dereference-null-ref.spec.ts

@@ -0,0 +1,14 @@
+import { describe, it } from "vitest";
+import { expect } from "vitest";
+import $RefParser from "../../../lib/index.js";
+import path from "../../utils/path";
+import dereferenced from "./dereferenced.js";
+
+describe("dereferencing a `$ref` that points to a `null` value", () => {
+  it.only("should dereference successfully", async () => {
+    const parser = new $RefParser();
+    const schema = await parser.dereference(path.rel("test/specs/dereference-null-ref/dereference-null-ref.yaml"));
+    expect(schema).to.equal(parser.schema);
+    expect(schema).to.deep.equal(dereferenced);
+  });
+});

test/specs/dereference-null-ref/dereference-null-ref.yaml

@@ -0,0 +1,8 @@
+components:
+  examples:
+    product:
+      value:
+        data:
+          admission:
+            $ref: "#/components/examples/product/value/data/pas"
+          pas: null

test/specs/dereference-null-ref/dereferenced.ts

@@ -0,0 +1,14 @@
+export default {
+  components: {
+    examples: {
+      product: {
+        value: {
+          data: {
+            admission: null,
+            pas: null,
+          },
+        },
+      },
+    },
+  },
+};