Please see the following code:
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import java.security.cert.CertPathValidatorException;

public class CPVTest {
    public static void main(String[] args) {
        Throwable[] causes = {
         new Throwable(),
         new Throwable("message"),
new Throwable("message", new Throwable()) };

        for (Throwable cause: causes) {
            CertPathValidatorException cpve =
           new CertPathValidatorException(cause);
        
            // from CertPathValidatorException(Throwable cause) spec:
            // The detail message is set to (cause==null ? null : cause.toString() )
            // (which typically contains the class and detail message of cause).
            String message = (cause == null ? null : cause.toString());
        
            System.out.println("expected message:" + message);
            System.out.println("getMessage():" + cpve.getMessage());
        }
    }
}
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Since b37 it's output is:
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expected message:java.lang.Throwable
getMessage():null
expected message:java.lang.Throwable: message
getMessage():null
expected message:java.lang.Throwable: message
getMessage():null
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