Error when rendering template chain with illegal include

[simon-abbott]

Describe the bug
When trying to render a template in strict mode with an illegal include (something that generates the error 'include-denied'), mjml throws the following error:

/app/node_modules/mjml-core/lib/index.js:664
        throw new ValidationError(`ValidationError: \n ${errors.map(e => e.formattedMessage).join('\n')}`, errors);
                                                                           ^

TypeError: Cannot read properties of null (reading 'formattedMessage')
    at /app/node_modules/mjml-core/lib/index.js:664:76
    at Array.map (<anonymous>)
    at mjml2html (/app/node_modules/mjml-core/lib/index.js:664:65)
    at mjml2html (/app/node_modules/mjml/lib/index.js:15:32)
    at render (file:///app/build.js:215:44)
    at processDir (file:///app/build.js:262:25)
    at async file:///app/build.js:270:1

To Reproduce
Steps to reproduce the behavior:

1. Create a set of three mjml files:

   <!-- templates/problem.mjml -->
   <mjml>
     <mj-body>
       <mj-include path="./common/problem2.mjml" />
     </mj-body>
   </mjml>

   <!-- templates/common/problem2.mjml -->
   <mjml>
     <mj-body>
       <mj-include path="../problem3.mjml" />
     </mj-body>
   </mjml>

   <!-- templates/problem3.mjml -->
   <mj-section>
     <mj-column>
       <mj-text>
         Oh no!
       </mj-text>
     </mj-column>
   </mj-section>

2. Render it to HTML by doing:

   import { readFileSync } from 'node:fs';
   import mjml2html from 'mjml';
   
   const filePath = './templates/problem.mjml';
   const raw = readFileSync(filePath, { encoding: 'utf-8' });
   await mjml2html(raw, {
     filePath,
     ignoreIncludes: false,
     includePath: './templates',
     validationLevel: 'strict',
   });

3. See error

Expected behavior
Rendering a template should not throw inside the error formatting logic.

MJML environment (please complete the following information):

• OS: macOS
• MJML Version: 5.4.0
• MJML tool used: mjml js api (import mjml2html from 'mjml')

Email sending environment(for rendering issues):
N/A

Affected email clients (for rendering issues):
N/A

Screenshots
N/A

Additional context
N/A