def prepare_props(title=None, height=None, width=None):
    """Prepare key plotting kwargs for passing to Altair, which d/n like None values."""
    props = {}
    if title:
        props["title"] = title  # None gets rendered as `None`
    if height:
        props["height"] = height  # None violates Vega JSON Schema
    if width:
        props["width"] = width  # None violates Vega JSON Schema
    return props