R1:226f3150933d

Fix PHP 8.1 "strlen(null)" exception creating Blueprint Working Copy

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. Phorge adopts `phutil_nonempty_string()` as a replacement, however use `phutil_nonempty_scalar()` as the value might not necessarily be a string object.

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