Fix PHP 8.1 DifferentialBranchField getBranchDescription strlen(null) error

Summary:
Fix PHP 8.1 strlen(null) error in DifferentialBranchField getBranchDescription()

Fixes T15531

Test Plan:
Simply viewing a diff (eg https://my.phorge.site/D1234) on a PHP 8.1 server generated the error fixed by this diff.

Also created a unit test.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15531

Differential Revision: https://we.phorge.it/D25335

src/__phutil_library_map__.php

@@ -466,6 +466,7 @@ phutil_register_library_map(array(
     'DifferentialBlockHeraldAction' => 'applications/differential/herald/DifferentialBlockHeraldAction.php',
     'DifferentialBlockingReviewerDatasource' => 'applications/differential/typeahead/DifferentialBlockingReviewerDatasource.php',
     'DifferentialBranchField' => 'applications/differential/customfield/DifferentialBranchField.php',
+    'DifferentialBranchFieldTestCase' => 'applications/differential/customfield/__tests__/DifferentialBranchFieldTestCase.php',
     'DifferentialBuildableEngine' => 'applications/differential/harbormaster/DifferentialBuildableEngine.php',
     'DifferentialChangeDetailMailView' => 'applications/differential/mail/DifferentialChangeDetailMailView.php',
     'DifferentialChangeHeraldFieldGroup' => 'applications/differential/herald/DifferentialChangeHeraldFieldGroup.php',
@@ -6472,6 +6473,7 @@ phutil_register_library_map(array(
     'DifferentialBlockHeraldAction' => 'HeraldAction',
     'DifferentialBlockingReviewerDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'DifferentialBranchField' => 'DifferentialCustomField',
+    'DifferentialBranchFieldTestCase' => 'PhabricatorTestCase',
     'DifferentialBuildableEngine' => 'HarbormasterBuildableEngine',
     'DifferentialChangeDetailMailView' => 'DifferentialMailView',
     'DifferentialChangeHeraldFieldGroup' => 'HeraldFieldGroup',

src/applications/differential/customfield/DifferentialBranchField.php

@@ -45,7 +45,7 @@ final class DifferentialBranchField
       return pht('%s (bookmark)', $bookmark);
     } else if (strlen($branch)) {
       $onto = $diff->loadTargetBranch();
-      if (strlen($onto) && ($onto !== $branch)) {
+      if (phutil_nonempty_string($onto) && ($onto !== $branch)) {
         return pht(
           '%s (branched from %s)',
           $branch,

src/applications/differential/customfield/__tests__/DifferentialBranchFieldTestCase.php

@@ -0,0 +1,39 @@
+<?php
+
+final class DifferentialBranchFieldTestCase extends PhabricatorTestCase {
+
+  protected function getPhabricatorTestCaseConfiguration() {
+    return array(
+      self::PHABRICATOR_TESTCONFIG_BUILD_STORAGE_FIXTURES => true,
+    );
+  }
+
+  private function getTestDiff() {
+  $parser = new ArcanistDiffParser();
+  $raw_diff = <<<EODIFF
+diff --git a/src b/src
+index 123457..bb216b1 100644
+--- a/src
++++ b/src
+@@ -1,5 +1,5 @@
+ Line a
+-Line b
++Line 2
+ Line c
+ Line d
+ Line e
+EODIFF;
+
+  return DifferentialDiff::newFromRawChanges(
+    PhabricatorUser::getOmnipotentUser(),
+    $parser->parseDiff($raw_diff));
+  }
+
+  public function testRenderDiffPropertyViewValue() {
+    $test_object = new DifferentialBranchField();
+    $diff = $this->getTestDiff();
+    $diff->setBranch('test');
+    $this->assertEqual('test',
+      $test_object->renderDiffPropertyViewValue($diff));
+  }
+}