Clarify sentinel URL examples in transport diagnostics docs

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

README.md

@@ -187,7 +187,7 @@ Polling timeouts and repeated polling failures are surfaced as:
 
 `HyperbrowserPollingError` also covers stalled pagination (no page-batch progress during result collection).
 Transport-level request failures include HTTP method + URL context in error messages.
-URL-like fallback objects are stringified for transport diagnostics; missing/malformed/sentinel URL inputs (for example `None` or numeric-only values) are normalized to `unknown URL`.
+URL-like fallback objects are stringified for transport diagnostics; missing/malformed/sentinel URL inputs (for example `None`, `null`/`undefined`/`nan`, or numeric-only values) are normalized to `unknown URL`.
 
 ```python
 from hyperbrowser import Hyperbrowser