diff --git a/src/test/scala/tlschannel/helpers/NullSslSession.java b/src/test/scala/tlschannel/helpers/NullSslSession.java
new file mode 100644
index 00000000..abc74bb5
--- /dev/null
+++ b/src/test/scala/tlschannel/helpers/NullSslSession.java
@@ -0,0 +1,116 @@
+package tlschannel.helpers;
+
+import java.security.Principal;
+import java.security.cert.Certificate;
+import javax.net.ssl.SSLSession;
+import javax.net.ssl.SSLSessionContext;
+import javax.security.cert.X509Certificate;
+
+public class NullSslSession implements SSLSession {
+
+    private final int bufferSize;
+
+    public NullSslSession(int bufferSize) {
+        this.bufferSize = bufferSize;
+    }
+
+    @Override
+    public byte[] getId() {
+        return new byte[0];
+    }
+
+    @Override
+    public SSLSessionContext getSessionContext() {
+        return null;
+    }
+
+    @Override
+    public long getCreationTime() {
+        return System.currentTimeMillis();
+    }
+
+    @Override
+    public long getLastAccessedTime() {
+        return System.currentTimeMillis();
+    }
+
+    @Override
+    public void invalidate() {}
+
+    @Override
+    public boolean isValid() {
+        return false;
+    }
+
+    @Override
+    public void putValue(String name, Object value) {}
+
+    @Override
+    public Object getValue(String name) {
+        return null;
+    }
+
+    @Override
+    public void removeValue(String name) {}
+
+    @Override
+    public String[] getValueNames() {
+        return new String[0];
+    }
+
+    @Override
+    public Certificate[] getPeerCertificates() {
+        return new Certificate[0];
+    }
+
+    @Override
+    public Certificate[] getLocalCertificates() {
+        return new Certificate[0];
+    }
+
+    @Override
+    public Principal getPeerPrincipal() {
+        return null;
+    }
+
+    @Override
+    public Principal getLocalPrincipal() {
+        return null;
+    }
+
+    @Override
+    public String getCipherSuite() {
+        return null;
+    }
+
+    @Override
+    public String getProtocol() {
+        return "";
+    }
+
+    @Override
+    public String getPeerHost() {
+        return null;
+    }
+
+    @Override
+    public int getPeerPort() {
+        return 0;
+    }
+
+    @Override
+    public int getPacketBufferSize() {
+        return 0;
+    }
+
+    @Override
+    public int getApplicationBufferSize() {
+        return bufferSize;
+    }
+
+    @Override
+    @SuppressWarnings("removal")
+    public X509Certificate[] getPeerCertificateChain() {
+        return new X509Certificate[0];
+    }
+}
diff --git a/src/test/scala/tlschannel/helpers/NullSslSession.scala b/src/test/scala/tlschannel/helpers/NullSslSession.scala
deleted file mode 100644
index 5f690e23..00000000
--- a/src/test/scala/tlschannel/helpers/NullSslSession.scala
+++ /dev/null
@@ -1,34 +0,0 @@
-package tlschannel.helpers
-
-import javax.net.ssl.SSLSession
-
-class NullSslSession(bufferSize: Int) extends SSLSession {
-
-  def getApplicationBufferSize() = bufferSize
-  def getCipherSuite() = null
-  def getCreationTime() = System.currentTimeMillis()
-  def getId() = Array()
-  def getLastAccessedTime() = System.currentTimeMillis()
-  def getLocalCertificates() = Array()
-  def getLocalPrincipal() = null
-  def getPacketBufferSize() = bufferSize
-
-  /** getPeerCertificateChain is a default method since Java 15, so we have to override to make the compiler happy (and
-    * still supply an implementation for earlier versions).
-    */
-  override def getPeerCertificateChain() = Array()
-
-  def getPeerCertificates() = Array()
-  def getPeerHost() = null
-  def getPeerPort() = 0
-  def getPeerPrincipal() = null
-  def getProtocol() = ""
-  def getSessionContext() = null
-  def getValue(s: String) = null
-  def getValueNames() = Array()
-  def invalidate() = {}
-  def isValid() = true
-  def putValue(k: String, v: Any) = {}
-  def removeValue(k: String) = {}
-
-}