diff --git a/src/applications/conduit/parametertype/ConduitListParameterType.php b/src/applications/conduit/parametertype/ConduitListParameterType.php
index 10c81e8c5d..6ec3898ac2 100644
--- a/src/applications/conduit/parametertype/ConduitListParameterType.php
+++ b/src/applications/conduit/parametertype/ConduitListParameterType.php
@@ -1,53 +1,71 @@
 <?php
 
 abstract class ConduitListParameterType
   extends ConduitParameterType {
 
+  private $allowEmptyList = true;
+
+  public function setAllowEmptyList($allow_empty_list) {
+    $this->allowEmptyList = $allow_empty_list;
+    return $this;
+  }
+
+  public function getAllowEmptyList() {
+    return $this->allowEmptyList;
+  }
+
   protected function getParameterValue(array $request, $key) {
     $value = parent::getParameterValue($request, $key);
 
     if (!is_array($value)) {
       $this->raiseValidationException(
         $request,
         $key,
         pht('Expected a list, but value is not a list.'));
     }
 
     $actual_keys = array_keys($value);
     if ($value) {
       $natural_keys = range(0, count($value) - 1);
     } else {
       $natural_keys = array();
     }
 
     if ($actual_keys !== $natural_keys) {
       $this->raiseValidationException(
         $request,
         $key,
         pht('Expected a list, but value is an object.'));
     }
 
+    if (!$value && !$this->getAllowEmptyList()) {
+      $this->raiseValidationException(
+        $request,
+        $key,
+        pht('Expected a nonempty list, but value is an empty list.'));
+    }
+
     return $value;
   }
 
   protected function validateStringList(array $request, $key, array $list) {
     foreach ($list as $idx => $item) {
       if (!is_string($item)) {
         $this->raiseValidationException(
           $request,
           $key,
           pht(
             'Expected a list of strings, but item with index "%s" is '.
             'not a string.',
             $idx));
       }
     }
 
     return $list;
   }
 
   protected function getParameterDefault() {
     return array();
   }
 
 }
diff --git a/src/applications/conduit/parametertype/ConduitParameterType.php b/src/applications/conduit/parametertype/ConduitParameterType.php
index 8f02057c0f..6468b099a0 100644
--- a/src/applications/conduit/parametertype/ConduitParameterType.php
+++ b/src/applications/conduit/parametertype/ConduitParameterType.php
@@ -1,97 +1,101 @@
 <?php
 
 /**
  * Defines how to read a value from a Conduit request.
  *
  * This class behaves like @{class:AphrontHTTPParameterType}, but for Conduit.
  */
 abstract class ConduitParameterType extends Phobject {
 
 
   private $viewer;
 
 
   final public function setViewer(PhabricatorUser $viewer) {
     $this->viewer = $viewer;
     return $this;
   }
 
 
   final public function getViewer() {
     if (!$this->viewer) {
       throw new PhutilInvalidStateException('setViewer');
     }
     return $this->viewer;
   }
 
 
   final public function getExists(array $request, $key) {
     return $this->getParameterExists($request, $key);
   }
 
 
   final public function getValue(array $request, $key) {
     if (!$this->getExists($request, $key)) {
       return $this->getParameterDefault();
     }
 
     return $this->getParameterValue($request, $key);
   }
 
 
   final public function getDefaultValue() {
     return $this->getParameterDefault();
   }
 
 
   final public function getTypeName() {
     return $this->getParameterTypeName();
   }
 
 
   final public function getFormatDescriptions() {
     return $this->getParameterFormatDescriptions();
   }
 
 
   final public function getExamples() {
     return $this->getParameterExamples();
   }
 
   protected function raiseValidationException(array $request, $key, $message) {
     // TODO: Specialize this so we can give users more tailored messages from
     // Conduit.
-    throw new Exception($message);
+    throw new Exception(
+      pht(
+        'Error while reading "%s": %s',
+        $key,
+        $message));
   }
 
 
   final public static function getAllTypes() {
     return id(new PhutilClassMapQuery())
       ->setAncestorClass(__CLASS__)
       ->setUniqueMethod('getTypeName')
       ->setSortMethod('getTypeName')
       ->execute();
   }
 
 
   protected function getParameterExists(array $request, $key) {
     return array_key_exists($key, $request);
   }
 
   protected function getParameterValue(array $request, $key) {
     return $request[$key];
   }
 
   abstract protected function getParameterTypeName();
 
 
   abstract protected function getParameterFormatDescriptions();
 
 
   abstract protected function getParameterExamples();
 
   protected function getParameterDefault() {
     return null;
   }
 
 }
diff --git a/src/applications/search/field/PhabricatorIDsSearchField.php b/src/applications/search/field/PhabricatorIDsSearchField.php
index 909cce9c4a..cb8c27ef75 100644
--- a/src/applications/search/field/PhabricatorIDsSearchField.php
+++ b/src/applications/search/field/PhabricatorIDsSearchField.php
@@ -1,30 +1,31 @@
 <?php
 
 final class PhabricatorIDsSearchField
   extends PhabricatorSearchField {
 
   protected function getDefaultValue() {
     return array();
   }
 
   protected function getValueFromRequest(AphrontRequest $request, $key) {
     return $request->getStrList($key);
   }
 
   protected function newControl() {
     if (strlen($this->getValueForControl())) {
       return new AphrontFormTextControl();
     } else {
       return null;
     }
   }
 
   protected function getValueForControl() {
     return implode(', ', parent::getValueForControl());
   }
 
   protected function newConduitParameterType() {
-    return new ConduitIntListParameterType();
+    return id(new ConduitIntListParameterType())
+      ->setAllowEmptyList(false);
   }
 
 }
diff --git a/src/applications/search/field/PhabricatorPHIDsSearchField.php b/src/applications/search/field/PhabricatorPHIDsSearchField.php
index 459233c472..c88ef7670a 100644
--- a/src/applications/search/field/PhabricatorPHIDsSearchField.php
+++ b/src/applications/search/field/PhabricatorPHIDsSearchField.php
@@ -1,30 +1,31 @@
 <?php
 
 final class PhabricatorPHIDsSearchField
   extends PhabricatorSearchField {
 
   protected function getDefaultValue() {
     return array();
   }
 
   protected function getValueFromRequest(AphrontRequest $request, $key) {
     return $request->getStrList($key);
   }
 
   protected function newControl() {
     if (strlen($this->getValueForControl())) {
       return new AphrontFormTextControl();
     } else {
       return null;
     }
   }
 
   protected function getValueForControl() {
     return implode(', ', parent::getValueForControl());
   }
 
   protected function newConduitParameterType() {
-    return new ConduitPHIDListParameterType();
+    return id(new ConduitPHIDListParameterType())
+      ->setAllowEmptyList(false);
   }
 
 }
diff --git a/src/applications/search/field/PhabricatorSearchDatasourceField.php b/src/applications/search/field/PhabricatorSearchDatasourceField.php
index 6ba322936f..d8c1242ef4 100644
--- a/src/applications/search/field/PhabricatorSearchDatasourceField.php
+++ b/src/applications/search/field/PhabricatorSearchDatasourceField.php
@@ -1,31 +1,32 @@
 <?php
 
 final class PhabricatorSearchDatasourceField
   extends PhabricatorSearchTokenizerField {
 
   private $datasource;
   private $conduitParameterType;
 
   protected function newDatasource() {
     return id(clone $this->datasource);
   }
 
   public function setDatasource(PhabricatorTypeaheadDatasource $datasource) {
     $this->datasource = $datasource;
     return $this;
   }
 
   public function setConduitParameterType(ConduitParameterType $type) {
     $this->conduitParameterType = $type;
     return $this;
   }
 
   protected function newConduitParameterType() {
     if (!$this->conduitParameterType) {
-      return new ConduitStringListParameterType();
+      return id(new ConduitStringListParameterType())
+        ->setAllowEmptyList(false);
     }
 
     return $this->conduitParameterType;
   }
 
 }