Prevent empty values in toc.yaml fields

**Description:**
`toc.yaml` should not allow fields with empty values.

**Current behavior:**
`toc.yaml` accepts fields with empty values (e.g., `name: ""`) without validation errors.

**Expected behavior:**
Validation should fail if any field in `toc.yaml` has an empty value.

**Steps to reproduce:**
1. Add a field with an empty value in `toc.yaml` (e.g., `name: ""`)
2. Run linting or validation

**Acceptance criteria:**
- Linting fails if any field in `toc.yaml` has an empty value
- Error message clearly indicates which field and its location are invalid