Merge branch 'fix_error_message' into 'master'

Fix wrong instance variable name in error message

See merge request !68
5 jobs for master in 7 minutes and 27 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #191232
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build_linux_36

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build_linux_37

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build_macosx_36

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passed #191231
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build_macosx_37

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  Deploy
passed #191234
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deploy_beta

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