geom_density2d: Internal error with None values in data

[ASmirnov-HORIS]

Example:

data = {
    'x': [0, 1, None],
    'y': [0, 1, None],
}
ggplot(data, aes('x', 'y')) + geom_density2d()

Output:

Internal error: NullPointerException : <no message>