This does not compile:

       lsst::fw::MaskedImage<PixelT, MaskT> convolvedImage = 
            lsst::fw::kernel::convolve(fooImage, kernel, 0, vw::NoEdgeExtension(), -1);

However, this does

    PixelT threshold = 0;
    lsst::fw::MaskedImage<PixelT, MaskT> convolvedImage = 
         lsst::fw::kernel::convolve(fooImage, kernel, threshold, vw::NoEdgeExtension(), -1);