diff --git a/src/applications/differential/conduit/DifferentialCreateDiffConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialCreateDiffConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialCreateDiffConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialCreateDiffConduitAPIMethod.php
@@ -55,6 +55,9 @@
   protected function execute(ConduitAPIRequest $request) {
     $viewer = $request->getUser();
     $change_data = $request->getValue('changes');
+    if ($change_data === null) {
+      throw new Exception(pht('Field "changes" must be non-empty.'));
+    }
 
     $changes = array();
     foreach ($change_data as $dict) {
diff --git a/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialCreateRawDiffConduitAPIMethod.php
@@ -26,6 +26,9 @@
   protected function execute(ConduitAPIRequest $request) {
     $viewer = $request->getUser();
     $raw_diff = $request->getValue('diff');
+    if ($raw_diff === null || !strlen($raw_diff)) {
+      throw new Exception(pht('Field "raw_diff" must be non-empty.'));
+    }
 
     $repository_phid = $request->getValue('repositoryPHID');
     if ($repository_phid) {
diff --git a/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
@@ -33,6 +33,9 @@
     }
 
     $corpus = $request->getValue('corpus');
+    if ($corpus === null || !strlen($corpus)) {
+      throw new Exception(pht('Field "corpus" must be non-empty.'));
+    }
     $field_map = $parser->parseFields($corpus);
 
     $errors = $parser->getErrors();
diff --git a/src/applications/differential/conduit/DifferentialSetDiffPropertyConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialSetDiffPropertyConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialSetDiffPropertyConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialSetDiffPropertyConduitAPIMethod.php
@@ -30,9 +30,22 @@
   }
 
   protected function execute(ConduitAPIRequest $request) {
+    $data = $request->getValue('data');
+    if ($data === null || !strlen($data)) {
+      throw new Exception(pht('Field "data" must be non-empty.'));
+    }
+
     $diff_id = $request->getValue('diff_id');
+    if ($diff_id === null) {
+      throw new Exception(pht('Field "diff_id" must be non-null.'));
+    }
+
     $name = $request->getValue('name');
-    $data = json_decode($request->getValue('data'), true);
+    if ($name === null || !strlen($name)) {
+      throw new Exception(pht('Field "name" must be non-empty.'));
+    }
+
+    $data = json_decode($data, true);
 
     self::updateDiffProperty($diff_id, $name, $data);
   }
diff --git a/src/applications/differential/editor/DifferentialTransactionEditor.php b/src/applications/differential/editor/DifferentialTransactionEditor.php
--- a/src/applications/differential/editor/DifferentialTransactionEditor.php
+++ b/src/applications/differential/editor/DifferentialTransactionEditor.php
@@ -218,7 +218,7 @@
 
           // No "$", to allow for branches like T123_demo.
           $match = null;
-          if (preg_match('/^T(\d+)/i', $branch, $match)) {
+          if ($branch !== null && preg_match('/^T(\d+)/i', $branch, $match)) {
             $task_id = $match[1];
             $tasks = id(new ManiphestTaskQuery())
               ->setViewer($this->getActor())
diff --git a/src/applications/files/conduit/FileUploadConduitAPIMethod.php b/src/applications/files/conduit/FileUploadConduitAPIMethod.php
--- a/src/applications/files/conduit/FileUploadConduitAPIMethod.php
+++ b/src/applications/files/conduit/FileUploadConduitAPIMethod.php
@@ -31,6 +31,9 @@
     $view_policy = $request->getValue('viewPolicy');
 
     $data = $request->getValue('data_base64');
+    if ($data === null) {
+      throw new Exception(pht('Field "data_base64" must be non-empty.'));
+    }
     $data = $this->decodeBase64($data);
 
     $params = array(
diff --git a/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php b/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
--- a/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
+++ b/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
@@ -515,7 +515,7 @@
       }
     }
 
-    if (!strlen($receiver_name)) {
+    if ($receiver_name === null || !strlen($receiver_name)) {
       throw new Exception(
         pht(
           'Call omits required "receiver" parameter. Specify the PHID '.
@@ -523,7 +523,7 @@
     }
 
     $message_type = $request->getValue('type');
-    if (!strlen($message_type)) {
+    if ($message_type === null || !strlen($message_type)) {
       throw new Exception(
         pht(
           'Call omits required "type" parameter. Specify the type of '.
diff --git a/src/applications/harbormaster/editor/HarbormasterBuildPlanEditEngine.php b/src/applications/harbormaster/editor/HarbormasterBuildPlanEditEngine.php
--- a/src/applications/harbormaster/editor/HarbormasterBuildPlanEditEngine.php
+++ b/src/applications/harbormaster/editor/HarbormasterBuildPlanEditEngine.php
@@ -103,7 +103,7 @@
         $key);
       $behavior_option = $object->getPlanProperty($storage_key);
 
-      if (!strlen($behavior_option)) {
+      if ($behavior_option === null || !strlen($behavior_option)) {
         $behavior_option = $behavior->getPlanOption($object)->getKey();
       }
 
diff --git a/src/applications/paste/conduit/PasteCreateConduitAPIMethod.php b/src/applications/paste/conduit/PasteCreateConduitAPIMethod.php
--- a/src/applications/paste/conduit/PasteCreateConduitAPIMethod.php
+++ b/src/applications/paste/conduit/PasteCreateConduitAPIMethod.php
@@ -43,7 +43,7 @@
     $title    = $request->getValue('title');
     $language = $request->getValue('language');
 
-    if (!strlen($content)) {
+    if ($content === null || !strlen($content)) {
       throw new ConduitException('ERR-NO-PASTE');
     }
 
diff --git a/src/applications/phriction/conduit/PhrictionCreateConduitAPIMethod.php b/src/applications/phriction/conduit/PhrictionCreateConduitAPIMethod.php
--- a/src/applications/phriction/conduit/PhrictionCreateConduitAPIMethod.php
+++ b/src/applications/phriction/conduit/PhrictionCreateConduitAPIMethod.php
@@ -25,9 +25,10 @@
 
   protected function execute(ConduitAPIRequest $request) {
     $slug = $request->getValue('slug');
-    if (!strlen($slug)) {
-      throw new Exception(pht('No such document.'));
+    if ($slug === null || !strlen($slug)) {
+      throw new Exception(pht('Field "slug" must be non-empty.'));
     }
+
     $doc = id(new PhrictionDocumentQuery())
       ->setViewer($request->getUser())
       ->withSlugs(array(PhabricatorSlug::normalize($slug)))
diff --git a/src/applications/phriction/conduit/PhrictionEditConduitAPIMethod.php b/src/applications/phriction/conduit/PhrictionEditConduitAPIMethod.php
--- a/src/applications/phriction/conduit/PhrictionEditConduitAPIMethod.php
+++ b/src/applications/phriction/conduit/PhrictionEditConduitAPIMethod.php
@@ -25,6 +25,9 @@
 
   protected function execute(ConduitAPIRequest $request) {
     $slug = $request->getValue('slug');
+    if ($slug === null || !strlen($slug)) {
+      throw new Exception(pht('Field "slug" must be non-empty.'));
+    }
 
     $doc = id(new PhrictionDocumentQuery())
       ->setViewer($request->getUser())
diff --git a/src/applications/phriction/conduit/PhrictionHistoryConduitAPIMethod.php b/src/applications/phriction/conduit/PhrictionHistoryConduitAPIMethod.php
--- a/src/applications/phriction/conduit/PhrictionHistoryConduitAPIMethod.php
+++ b/src/applications/phriction/conduit/PhrictionHistoryConduitAPIMethod.php
@@ -38,6 +38,10 @@
 
   protected function execute(ConduitAPIRequest $request) {
     $slug = $request->getValue('slug');
+    if ($slug === null || !strlen($slug)) {
+      throw new Exception(pht('Field "slug" must be non-empty.'));
+    }
+
     $doc = id(new PhrictionDocumentQuery())
       ->setViewer($request->getUser())
       ->withSlugs(array(PhabricatorSlug::normalize($slug)))
diff --git a/src/applications/phriction/conduit/PhrictionInfoConduitAPIMethod.php b/src/applications/phriction/conduit/PhrictionInfoConduitAPIMethod.php
--- a/src/applications/phriction/conduit/PhrictionInfoConduitAPIMethod.php
+++ b/src/applications/phriction/conduit/PhrictionInfoConduitAPIMethod.php
@@ -38,6 +38,9 @@
 
   protected function execute(ConduitAPIRequest $request) {
     $slug = $request->getValue('slug');
+    if ($slug === null || !strlen($slug)) {
+      throw new Exception(pht('Field "slug" must be non-empty.'));
+    }
 
     $document = id(new PhrictionDocumentQuery())
       ->setViewer($request->getUser())
diff --git a/src/applications/project/conduit/ProjectCreateConduitAPIMethod.php b/src/applications/project/conduit/ProjectCreateConduitAPIMethod.php
--- a/src/applications/project/conduit/ProjectCreateConduitAPIMethod.php
+++ b/src/applications/project/conduit/ProjectCreateConduitAPIMethod.php
@@ -43,12 +43,21 @@
 
     $project = PhabricatorProject::initializeNewProject($user);
     $type_name = PhabricatorProjectNameTransaction::TRANSACTIONTYPE;
+
+    $name = $request->getValue('name');
+    if ($name === null || !strlen(name)) {
+      throw new Exception(pht('Field "name" must be non-empty.'));
+    }
+
     $members = $request->getValue('members');
+    if ($members === null) {
+      $members = array();
+    }
     $xactions = array();
 
     $xactions[] = id(new PhabricatorProjectTransaction())
       ->setTransactionType($type_name)
-      ->setNewValue($request->getValue('name'));
+      ->setNewValue($name);
 
     if ($request->getValue('icon')) {
       $xactions[] = id(new PhabricatorProjectTransaction())
diff --git a/src/applications/remarkup/conduit/RemarkupProcessConduitAPIMethod.php b/src/applications/remarkup/conduit/RemarkupProcessConduitAPIMethod.php
--- a/src/applications/remarkup/conduit/RemarkupProcessConduitAPIMethod.php
+++ b/src/applications/remarkup/conduit/RemarkupProcessConduitAPIMethod.php
@@ -41,7 +41,7 @@
 
     $engine_class = idx($this->getEngineContexts(), $context);
     if (!$engine_class) {
-      throw new ConduitException('ERR-INVALID_ENGINE');
+      throw new ConduitException('ERR-INVALID-ENGINE');
     }
 
     $engine = PhabricatorMarkupEngine::$engine_class();
diff --git a/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php b/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
--- a/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
+++ b/src/applications/transactions/editengine/PhabricatorEditEngineAPIMethod.php
@@ -95,7 +95,7 @@
       $section[] = $type->getConduitDescription();
 
       $type_documentation = $type->getConduitDocumentation();
-      if (strlen($type_documentation)) {
+      if ($type_documentation !== null && strlen($type_documentation)) {
         $section[] = $type_documentation;
       }
 
diff --git a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldInt.php b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldInt.php
--- a/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldInt.php
+++ b/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldInt.php
@@ -24,7 +24,7 @@
 
   public function getValueForStorage() {
     $value = $this->getFieldValue();
-    if (strlen($value)) {
+    if ($value !== null && strlen($value)) {
       return $value;
     } else {
       return null;
diff --git a/src/infrastructure/markup/blockrule/PhutilRemarkupTableBlockRule.php b/src/infrastructure/markup/blockrule/PhutilRemarkupTableBlockRule.php
--- a/src/infrastructure/markup/blockrule/PhutilRemarkupTableBlockRule.php
+++ b/src/infrastructure/markup/blockrule/PhutilRemarkupTableBlockRule.php
@@ -114,7 +114,7 @@
         if ($cell->isContentNode()) {
           $content = $node->getContent();
 
-          if (!strlen(trim($content))) {
+          if ($content === null || !strlen(trim($content))) {
             continue;
           }