R1:bab997074055

Fix PHP 8.1 "trim(null)" exception which blocks rendering Conduit's harbormaster.sendmessage page

Summary:
Since PHP 8.1, passing a null string to `trim()` is deprecated.
Thus first check that `$content` is not null before trimming it.

Also since trim() returns a string and never null, we can also simplify the non-empty check,
in a more readable and efficient way, avoiding strlen() that was usually used for other "more wild" cases.

```
EXCEPTION: (RuntimeException) trim(): Passing null to parameter #1…