diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
index d010f219..8f866bb1 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
@@ -50,8 +50,8 @@ public class Certificate extends AcmeResource {
     private static final long serialVersionUID = 7381527770159084201L;
     private static final Logger LOG = LoggerFactory.getLogger(Certificate.class);
 
-    private ArrayList<X509Certificate> certChain = null;
-    private ArrayList<URL> alternates = null;
+    private ArrayList<X509Certificate> certChain;
+    private ArrayList<URL> alternates;
 
     protected Certificate(Login login, URL certUrl) {
         super(login, certUrl);
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java b/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
index 3560de1e..bd94c7b6 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
@@ -457,7 +457,7 @@ public class DefaultConnection implements Connection {
     private void throwAcmeException() throws AcmeException {
         try {
             String contentType = AcmeUtils.getContentType(conn.getHeaderField(CONTENT_TYPE_HEADER));
-            if (!"application/problem+json".equals(contentType)) {
+            if (!MIME_JSON_PROBLEM.equals(contentType)) {
                 throw new AcmeException("HTTP " + conn.getResponseCode() + ": " + conn.getResponseMessage());
             }
 
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleHttpConnector.java b/acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleHttpConnector.java
index 6a0ef451..cff21e12 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleHttpConnector.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleHttpConnector.java
@@ -26,10 +26,8 @@ import java.security.cert.CertificateException;
 
 import javax.annotation.ParametersAreNonnullByDefault;
 import javax.annotation.concurrent.ThreadSafe;
-import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.HttpsURLConnection;
 import javax.net.ssl.SSLContext;
-import javax.net.ssl.SSLSession;
 import javax.net.ssl.SSLSocketFactory;
 import javax.net.ssl.TrustManagerFactory;
 
@@ -42,14 +40,6 @@ import org.shredzone.acme4j.connector.HttpConnector;
 @ParametersAreNonnullByDefault
 @ThreadSafe
 public class PebbleHttpConnector extends HttpConnector {
-
-    private static HostnameVerifier ALLOW_ALL_HOSTNAME_VERIFIER = new HostnameVerifier() {
-        @Override
-        public boolean verify(String hostname, SSLSession session) {
-            return true;
-        }
-    };
-
     private static SSLSocketFactory sslSocketFactory;
 
     @Override
@@ -58,7 +48,7 @@ public class PebbleHttpConnector extends HttpConnector {
         if (conn instanceof HttpsURLConnection) {
             HttpsURLConnection conns = (HttpsURLConnection) conn;
             conns.setSSLSocketFactory(createSocketFactory());
-            conns.setHostnameVerifier(ALLOW_ALL_HOSTNAME_VERIFIER);
+            conns.setHostnameVerifier((hostname, session) -> true);
         }
         return conn;
     }