How to use the datashader.glyphs.glyph.isnull function in datashader

def perform_extend(i, sx, tx, sy, ty, xmin, xmax, ymin, ymax, plot_start,
                       xs, ys0, ys1, *aggs_and_cols):
        x0 = xs[i]
        x1 = xs[i + 1]
        y0 = ys0[i]
        y1 = ys1[i]
        y2 = ys1[i + 1]
        y3 = ys0[i + 1]
        trapezoid_start = (plot_start if i == 0 else
                           (isnull(xs[i - 1]) or
                            isnull(ys0[i - 1]) or
                            isnull(ys1[i - 1])))
        stacked = True
        draw_trapezoid_y(
            i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            x0, x1, y0, y1, y2, y3, trapezoid_start, stacked,
            *aggs_and_cols
        )

def perform_extend_line(
            i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax, xs, ys, *aggs_and_cols
    ):
        x0 = xs[i, j]
        y0 = ys[j]
        x1 = xs[i, j + 1]
        y1 = ys[j + 1]

        segment_start = (
                (j == 0) or isnull(xs[i, j - 1]) or isnull(ys[j - 1])
        )

        draw_segment(i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
                     segment_start, x0, x1, y0, y1, *aggs_and_cols)

def perform_extend_line(
            i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax, xs, ys, *aggs_and_cols
    ):
        x0 = xs[j]
        y0 = ys[i, j]
        x1 = xs[j + 1]
        y1 = ys[i, j + 1]

        segment_start = (
                (j == 0) or isnull(xs[j - 1]) or isnull(ys[i, j - 1])
        )

        draw_segment(i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
                     segment_start, x0, x1, y0, y1, *aggs_and_cols)

def perform_extend_line(
            i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            xs, ys, *aggs_and_cols
    ):
        x0 = xs[i, j]
        y0 = ys[i, j]
        x1 = xs[i, j + 1]
        y1 = ys[i, j + 1]
        segment_start = (
                (j == 0) or isnull(xs[i, j - 1]) or isnull(ys[i, j - 1])
        )

        draw_segment(i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
                     segment_start, x0, x1, y0, y1, *aggs_and_cols)

def draw_segment(
            i, sx, tx, sy, ty, xmin, xmax, ymin, ymax, segment_start,
            x0, x1, y0, y1, *aggs_and_cols
    ):
        """Draw a line segment using Bresenham's algorithm
        This method plots a line segment with integer coordinates onto a pixel
        grid.
        """
        skip = False

        # If any of the coordinates are NaN, there's a discontinuity.
        # Skip the entire segment.
        if isnull(x0) or isnull(y0) or isnull(x1) or isnull(y1):
            skip = True

        # Use Liang-Barsky (1992) to clip the segment to a bounding box
        # Check if line is fully outside viewport
        if x0 < xmin and x1 < xmin:
            skip = True
        elif x0 > xmax and x1 > xmax:
            skip = True
        elif y0 < ymin and y1 < ymin:
            skip = True
        elif y0 > ymax and y1 > ymax:
            skip = True

        t0, t1 = 0, 1
        dx1 = x1 - x0
        t0, t1, accept = _clipt(-dx1, x0 - xmin, t0, t1)

def perform_extend(
            i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            xs, ys, *aggs_and_cols
    ):
        x0 = xs[i, j]
        x1 = xs[i, j + 1]

        y0 = ys[i, j]
        y1 = 0.0
        y2 = 0.0
        y3 = ys[i, j + 1]

        trapezoid_start = (j == 0 or
                           isnull(xs[i, j - 1]) or
                           isnull(ys[i, j - 1]))
        stacked = False
        draw_trapezoid_y(
            i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            x0, x1, y0, y1, y2, y3, trapezoid_start, stacked, *aggs_and_cols
        )

def perform_extend(
            i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            xs, ys, *aggs_and_cols
    ):
        x0 = xs[i, j]
        x1 = xs[i, j + 1]

        y0 = ys[i, j]
        y1 = 0.0
        y2 = 0.0
        y3 = ys[i, j + 1]

        trapezoid_start = (j == 0 or
                           isnull(xs[i, j - 1]) or
                           isnull(ys[i, j - 1]))
        stacked = False
        draw_trapezoid_y(
            i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            x0, x1, y0, y1, y2, y3, trapezoid_start, stacked, *aggs_and_cols
        )

def perform_extend(i, j, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
                       xs, ys, *aggs_and_cols):

        x0 = xs[j]
        x1 = xs[j + 1]

        y0 = ys[i, j]
        y1 = 0.0
        y2 = 0.0
        y3 = ys[i, j + 1]

        trapezoid_start = (j == 0 or
                           isnull(xs[j - 1]) or
                           isnull(ys[i, j - 1]))
        stacked = False
        draw_trapezoid_y(
            i, sx, tx, sy, ty, xmin, xmax, ymin, ymax,
            x0, x1, y0, y1, y2, y3, trapezoid_start, stacked,
            *aggs_and_cols
        )