Classic Engine Evaluation Semantics (vs. failing SBE Semantics):

• If 'input' is nullish, return a null value (SBE - checked in the builtinTrim function)
• else if 'input' is not null but is a non-string value, throw an error (SBE - throws an error assuming previous condition is validated)
• else if 'chars' is not provided, trim with default whitespace characters (SBE - trims with default whitespace characters)
• else if 'chars' is provided and null, return a null value (SBE INCORRECT - treats this as the same as not providing it at all)
• else if 'chars' is provided and not a string, throw an error (SBE - throws an error)
• else perform trim on 'input' with 'chars' (SBE - trims with 'chars')

Fix: Treat null 'chars' as different from no 'chars' given and make sure null 'input' is checking before !isString (completed)