diff --git a/src/utils/utils.php b/src/utils/utils.php
--- a/src/utils/utils.php
+++ b/src/utils/utils.php
@@ -2184,6 +2184,9 @@
  * string other than the empty string, integers, and floats are considered
  * scalar.
  *
+ * Note that booleans are also valid scalars, where false is considered empty,
+ * and true is non-empty since if you cast true to string, it's non-empty.
+ *
  * This method raises an exception if passed any other value.
  *
  * @param Value to test.
@@ -2202,6 +2205,14 @@
     return true;
   }
 
+  // Booleans are also valid scalars by PHP. Inventing the opposite can be
+  // too much esoteric and problematic.
+  //   false: empty,     because casted to string becomes ''  (empty)
+  //   true:  non-empty, because casted to string becomes '1' (non-empty)
+  if ($value === false || $value === true) {
+    return $value;
+  }
+
   if (is_object($value)) {
     try {
       $string = phutil_string_cast($value);