Don't remove null type if a default is present.

Author: luhn

packages/openapi-typescript/examples/github-api-next.ts

@@ -108750,7 +108750,7 @@ export interface operations {
                 /** @description The name of the task for the deployment (e.g., `deploy` or `deploy:migrations`). */
                 task?: string;
                 /** @description The name of the environment that was deployed to (e.g., `staging` or `production`). */
-                environment?: string;
+                environment?: string | null;
                 /** @description The number of results per page (max 100). For more information, see "[Using pagination in the REST API](https://docs.github.com/rest/using-the-rest-api/using-pagination-in-the-rest-api)." */
                 per_page?: components["parameters"]["per-page"];
                 /** @description The page number of the results to fetch. For more information, see "[Using pagination in the REST API](https://docs.github.com/rest/using-the-rest-api/using-pagination-in-the-rest-api)." */

packages/openapi-typescript/src/transform/schema-object.ts

@@ -405,9 +405,7 @@ function transformSchemaObjectCore(schemaObject: SchemaObject, options: Transfor
       } else {
         for (const t of schemaObject.type) {
           if (t === "null" || t === null) {
-            if (!schemaObject.default) {
-              uniqueTypes.push(NULL);
-            }
+            uniqueTypes.push(NULL);
           } else {
             uniqueTypes.push(transformSchemaObject({ ...schemaObject, type: t } as SchemaObject, options));
           }

packages/openapi-typescript/test/transform/schema-object/string.test.ts

@@ -102,7 +102,7 @@ describe("transformSchemaObject > string", () => {
       "default + nullable",
       {
         given: { type: ["string", "null"], default: "en" },
-        want: "string",
+        want: "string | null",
       },
     ],
     [