imagick: setStrokeDashArray(null)

[MatthiasKuehneEllerhold]

With Imagick 3.8.0 you can pass null to setStrokeDashArray() in order to reset the dash array.
See Imagick/imagick@c555f5e

ImageMagick 6 accepted [null], but ImageMagick 7 needs null for it to work.
Otherwise this ImagickException is thrown:

non-conforming drawing primitive definition `stroke-dasharray' @ error/draw.c/RenderMVGContent/4548