diff --git a/src/Util/Cache.php b/src/Util/Cache.php
index 68abef59c4..a316bc9ac9 100644
--- a/src/Util/Cache.php
+++ b/src/Util/Cache.php
@@ -266,7 +266,7 @@ function ($file, $key, $iterator) {
             self::$cache = json_decode(file_get_contents(self::$path), true);
 
             // Verify the contents of the cache file.
-            if (self::$cache['config'] !== $configData) {
+            if (self::$cache === null || self::$cache['config'] !== $configData) {
                 self::$cache = [];
                 if (PHP_CODESNIFFER_VERBOSITY > 1) {
                     echo "\t* cache was invalid and has been cleared *".PHP_EOL;