If a color value of ['', '', 'NONE', 'NONE', ''] is given as value to
the highlighting group, the resulting group definition would look like
this:
hi Normal ctermfg=NONE ctermbg=NONE
which would result in the highlighting group being cleared (or even no
set at all), therefore check that at least one other value exists and if
not fall back to the highlighting definition of the Normal group.
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