Gradient with constant value not showing

[Azraelless]

When the values in data are identical adding gradient to it makes it disappear. If I change one of the points in data chart appears. If I remove gradient it shows as well.

Am I doing something wrong or is it a bug?

That code don't show chart:

          <Sparklines data={[1, 1, 1, 1, 1]}>
            <defs>
               <linearGradient id="s#212121" x1="0%" x2="100%">
                 <stop offset="0%" stopColor="#21212120" />
                 <stop offset="50%" stopColor="#21212180" />
                 <stop offset="100%" stopColor="#212121" />
               </linearGradient>
             </defs>
             <SparklinesLine style={{ fill: 'none' }} color="url(#s#212121)" />
           </Sparklines>