When I am plotting a feature plot and doing split by with Sample, this warning coming out -

Warning messages:
1: In FeaturePlot(data, features = c("gene1"), split.by = "Sample",  :
  All cells have the same value (0) of gene1.

Was does that means that there is no gene expression. If there is actually no expession. beacuse when i doing without splitby , its working fine.

can anyone suggest , what actually the interpretation of this Warning?