Description

It appears that the check for ensuring whether the evaluation output is for the stepper is missing (presumably removed as it is no longer in use), and the check falsely assumes an array with first element being an object (which unfortunately, arrays are objects as well) is stepper output, and then tries to render the stepper with invalid information

Some examples include:
pair(pair(1, 2), 3);
list(list(1), 2);
list(pair(1, 2), 3);
pair(list(1), 2);

Resolves #3279.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Code quality improvements

How to test

Checklist

• I have tested this code
• I have updated the documentation