code: @OverrideOnDemand
    protected void hashCodeLinkedException (@Nonnull final HashCodeGenerator aHCG, @Nullable final Throwable t)
    {
      if (t == null)
        aHCG.append (HashCodeCalculator.HASHCODE_NULL);
      else
        aHCG.append (t.getClass ()).append (t.getMessage ());
    }
docs: Overridable implementation of Throwable for the Linked exception field.
  This can be overridden to implement a different algorithm. This is
  customizable because there is no default way of hashing Exceptions in Java.
  If you override this method you must also override
  {@link #equalsLinkedException(Throwable, Throwable)}!
  
  @param aHCG
  The hash code generator to append to. Never <code>null</code>.
  @param t
  The Throwable to append. May be <code>null</code>.