R1:19d9da7feae9

Fix PHP 8.1 "strlen(null)" exception which blocks Working Copy blueprint creation in Drydock

Summary:
`strlen()` was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. So, we adopt an explicit cast to string
in order to answer the question "Is this a non-empty string?" without relying on implicit
cast and deprecated things.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If…