Contrasts error

when running wf with:

• bwl-dpi-covar.csv
• bwl-dpi-pheno.csv

Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : 
    contrasts can be applied only to factors with 2 or more levels
  Calls: <Anonymous> ... model.matrix -> model.matrix.default -> contrasts<-
  Execution halted

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