diff --git a/src/main/java/io/jenkins/plugins/emmenthal/SsrfBuilder.java b/src/main/java/io/jenkins/plugins/emmenthal/SsrfBuilder.java
index 885ac13..5a71850 100644
--- a/src/main/java/io/jenkins/plugins/emmenthal/SsrfBuilder.java
+++ b/src/main/java/io/jenkins/plugins/emmenthal/SsrfBuilder.java
@@ -82,6 +82,7 @@ public FormValidation doCheckUrl(@QueryParameter String value) throws IOExceptio
             Jenkins.get().checkPermission(Job.CONFIGURE);
             value = Util.fixEmptyAndTrim(value);
 
+            assert value != null;
             URL url = new URL(value);
             HttpURLConnection con = (HttpURLConnection) url.openConnection();
             con.setRequestMethod("GET");
diff --git a/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithCredsBuilder.java b/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithCredsBuilder.java
index cfbb32d..5cb6a28 100644
--- a/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithCredsBuilder.java
+++ b/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithCredsBuilder.java
@@ -121,7 +121,8 @@ public FormValidation doValidateUrlAndCredentialsId(@AncestorInPath Item item, @
                     CredentialsProvider.lookupCredentials(StandardUsernamePasswordCredentials.class, item,
                             ACL.SYSTEM, Collections.emptyList()),
                     CredentialsMatchers.withId(credentialsId));
-            
+
+            assert url != null;
             URL urlObject = new URL(url);
             HttpURLConnection con = (HttpURLConnection) urlObject.openConnection();
             con.setRequestMethod("GET");
diff --git a/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithPasswordBuilder.java b/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithPasswordBuilder.java
index 370a8d7..56fefa4 100644
--- a/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithPasswordBuilder.java
+++ b/src/main/java/io/jenkins/plugins/emmenthal/SsrfWithPasswordBuilder.java
@@ -108,6 +108,7 @@ public FormValidation doValidateUrlAndAuth(@QueryParameter String url,
             Jenkins.get().checkPermission(Job.CONFIGURE);
             url = Util.fixEmptyAndTrim(url);
 
+            assert url != null;
             URL urlObject = new URL(url);
             HttpURLConnection con = (HttpURLConnection) urlObject.openConnection();
             con.setRequestMethod("GET");