Upgrade ImageMagick to more recent version.
Current version is 6.8.9-9 released in 2014, so quite outdated. A more current version like 6.9.10 or 6.9.11 would be more suitable and also fix a lot of small bugs.
15
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With new Hypernodes running on Debian Buster we also made it possible to use version 6.9.10 of ImageMagick