src/java.base/share/classes/java/lang/Throwable.java

@@ -464,10 +464,20 @@
             throw new IllegalArgumentException("Self-causation not permitted", this);
         this.cause = cause;
         return this;
     }
 
+    /*
+     * This is called by readObject of a few exceptions such as
+     * ClassNotFoundException and ExceptionInInitializerError to deserialize
+     * a stream output from an older runtime version where the cause may
+     * have set to null.
+     */
+    void setCause(Throwable t) {
+        this.cause = t;
+    }
+
     /**
      * Returns a short description of this throwable.
      * The result is the concatenation of:
      * <ul>
      * <li> the {@linkplain Class#getName() name} of the class of this object