diff --git a/src/Validator/InputValidator.php b/src/Validator/InputValidator.php
index 013fd45b..05bc4740 100644
--- a/src/Validator/InputValidator.php
+++ b/src/Validator/InputValidator.php
@@ -138,6 +138,12 @@ private function buildValidationTree(ValidationNode $rootObject, iterable $field
 
         foreach ($fields as $name => $arg) {
             $property = $arg['name'] ?? $name;
+
+            if (!array_key_exists($property, $inputData)) {
+                // This field was not provided in the inputData. Do not attempt to validate it.
+                continue;
+            }
+            
             $config = static::normalizeConfig($arg['validation'] ?? []);
 
             if (isset($config['cascade']) && isset($inputData[$property])) {