diff --git a/phpunit.xml b/phpunit.xml
index 84820b6..85c21b7 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -5,6 +5,7 @@
          convertErrorsToExceptions="true"
          convertNoticesToExceptions="true"
          convertWarningsToExceptions="true"
+         cacheResult="false"
          stopOnError="false"
          stopOnFailure="false"
 >
diff --git a/src/GitVersion.php b/src/GitVersion.php
index 4a864f3..7f09aec 100644
--- a/src/GitVersion.php
+++ b/src/GitVersion.php
@@ -79,9 +79,9 @@ public function getBranch(): ?string
 
     /**
      * Get the latest commit ID.
-     * @return string
+     * @return string|null
      */
-    public function getCommit(): string
+    public function getCommit(): ?string
     {
         if ($this->commit === null && $this->isRepo()) {
             /**