fmodata: Nested expand generates empty $select= causing OData parse error

[eluce2]

Description

When using nested expand() calls without explicit select(), the library generates an empty $select= statement which FileMaker OData cannot parse.

Reproduction

import { fmTableOccurrence, textField, containerField, FMServerConnection } from "@proofkit/fmodata";

const Parent = fmTableOccurrence("Parent", {
  _pk: textField().primaryKey().entityId("FMFID:1"),
}, {
  entityId: "FMTID:1",
  navigationPaths: ["Child"],
});

const Child = fmTableOccurrence("Child", {
  _pk: textField().primaryKey().entityId("FMFID:2"),
  data: textField().entityId("FMFID:3"),
}, {
  entityId: "FMTID:2",
  navigationPaths: ["Parent"],
});

const connection = new FMServerConnection({
  serverUrl: "https://example.com",
  auth: { username: "test", password: "test" },
});

const db = connection.database("Test.fmp12", { useEntityIds: true });

// This generates invalid URL
const query = db
  .from(Parent)
  .get("test-id")
  .expand(Child);

console.log(query.getQueryString());
// Output: /FMTID:1('test-id')?$select=FMFID:1&$expand=FMTID:2($select=)
//                                                              ^^^^^^^^^ empty select

Expected behavior

Either:

1. Omit $select= entirely when no fields are selected
2. Or include all fields by default

Actual behavior

Generates $select=) which causes FileMaker OData to return:

OData error: Error: parse failure in URL at: ')'

Workaround

Explicitly call .select() with at least one field on every expand:

const query = db
  .from(Parent)
  .get("test-id")
  .expand(Child, (b) => b.select({ data: Child.data }));

Environment

• @proofkit/fmodata version: 0.1.0-beta.24
• FileMaker Server OData API