gitea: take a rule's null contexts as the forge's type says, so the strict build the checker runs compiles (issue 1891)

The checker builds a package with a build script by its tsconfig (strict),
where requiredOf and TrunkForge's appliedProtection said
status_check_contexts is string[] and BranchProtection says string[] | null:
four TS2345 errors, hidden on main behind earlier failures. Types only; the
emitted code is the same, and a test holds that null contexts require nothing.

modules/gitea/pulls.ts

@@ -25,7 +25,7 @@ export const CHECK_STATUS = "mesh/check";
 
 /** The statuses a branch's rule requires, from the rule the forge applies to it: none when it is unprotected or checks
  *  no status; undefined when the rule could not be read. */
-export function requiredOf(rule: { enable_status_check?: boolean; status_check_contexts?: string[] } | null | undefined): string[] | undefined {
+export function requiredOf(rule: { enable_status_check?: boolean; status_check_contexts?: string[] | null } | null | undefined): string[] | undefined {
   if (rule === undefined) return undefined;
   if (!rule || !rule.enable_status_check) return [];
   return (rule.status_check_contexts ?? []).filter(Boolean);

modules/gitea/test/pulls.test.ts

@@ -216,3 +216,12 @@ test("a base's required statuses decide which of the controller's statuses are w
   const comment = commentFor(c, {}, ["mesh/repo-check"]);
   assert.ok(comment === null || !comment.includes("mesh/merge-gate"), comment ?? "");
 });
+
+test("a rule the forge gives with no contexts (null) requires nothing, and an unread rule is unknown", async () => {
+  const { requiredOf } = await import("../pulls.ts");
+  // The forge's BranchProtection says status_check_contexts may be null (protection.ts); requiredOf takes it as it comes.
+  assert.deepEqual(requiredOf({ enable_status_check: true, status_check_contexts: null }), []);
+  assert.deepEqual(requiredOf({ enable_status_check: true, status_check_contexts: ["mesh/check", ""] }), ["mesh/check"]);
+  assert.deepEqual(requiredOf(null), []);
+  assert.equal(requiredOf(undefined), undefined);
+});

modules/gitea/trunk.ts

@@ -128,7 +128,7 @@ export interface TrunkForge {
   branchHead(owner: string, repo: string, branch: string): Promise<string>;
   /** The rule the forge applies to a branch: which of the controller's statuses are kept there (issue 1301). Not given,
    *  or not read: both, as before. */
-  appliedProtection?(owner: string, repo: string, branch: string): Promise<{ enable_status_check?: boolean; status_check_contexts?: string[] } | null>;
+  appliedProtection?(owner: string, repo: string, branch: string): Promise<{ enable_status_check?: boolean; status_check_contexts?: string[] | null } | null>;
 }
 
 /** What it writes with: the merge check's one writer (gate.ts), which decides in the head's own turn. */