Fix some PHP 8.1 issues in Diviner generator

Summary:
After this change I was able to generate again the Diviner
documentation from PHP 8.2 using the related command:

    ./bin/diviner generate

Closes T15255

Test Plan:
- run `./bin/diviner generate` - great success
- tested the advanced search in various ways - it still works

Reviewers: O1 Blessed Committers, Matthew

Reviewed By: O1 Blessed Committers, Matthew

Subscribers: Ekubischta, speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15226, T15255

Differential Revision: https://we.phorge.it/D25124

src/applications/diviner/query/DivinerBookQuery.php

@@ -133,7 +133,7 @@ final class DivinerBookQuery extends PhabricatorCursorPagedPolicyAwareQuery {
         $this->phids);
     }
 
-    if (strlen($this->nameLike)) {
+    if (phutil_nonempty_string($this->nameLike)) {
       $where[] = qsprintf(
         $conn,
         'name LIKE %~',
@@ -147,7 +147,7 @@ final class DivinerBookQuery extends PhabricatorCursorPagedPolicyAwareQuery {
         $this->names);
     }
 
-    if (strlen($this->namePrefix)) {
+    if (phutil_nonempty_string($this->namePrefix)) {
       $where[] = qsprintf(
         $conn,
         'name LIKE %>',

src/applications/diviner/storage/DivinerLiveSymbol.php

@@ -182,7 +182,7 @@ final class DivinerLiveSymbol extends DivinerDAO
   public function setTitle($value) {
     $this->writeField('title', $value);
 
-    if (strlen($value)) {
+    if (phutil_nonempty_string($value)) {
       $slug = DivinerAtomRef::normalizeTitleString($value);
       $hash = PhabricatorHash::digestForIndex($slug);
       $this->titleSlugHash = $hash;

src/applications/diviner/workflow/DivinerGenerateWorkflow.php

@@ -194,7 +194,7 @@ final class DivinerGenerateWorkflow extends DivinerWorkflow {
 
     $identifier = $args->getArg('repository');
     $repository = null;
-    if (strlen($identifier)) {
+    if (phutil_nonempty_string($identifier)) {
       $repository = id(new PhabricatorRepositoryQuery())
         ->setViewer(PhabricatorUser::getOmnipotentUser())
         ->withIdentifiers(array($identifier))