ERROR findmarkers latent.vars MAST

[Flu09]

I have a question and an issue regarding MAST latent variables

Idents(object) <- "celltype.condition"
markers <- FindMarkers(object,
                              ident.1 = "astro_DS",
                              ident.2 = "astro_CT",
                              assay = "RNA",
                              logfc.threshold	= 0,
                              test.use = 	"MAST",
                              latent.vars	= c("Age_at_death", "Sex") 
   
  Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : 
  contrasts can be applied only to factors with 2 or more levels
Calls: FindMarkers ... model.matrix -> model.matrix.default -> contrasts<-
Execution halted

the age at death is character. Do I need to change to numeric before using the findmarkers function to find DEGS between disease and control?

str(object$Age_at_death) Named chr [1:309364] "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" "82" ...

• attr(*, "names")= chr [1:309364] "D03_S09_AAACCTGAGCTTTGGT-1" "D03_S09_AAACCTGAGGCCCTTG-1" "D03_S09_AAACCTGAGTAGCGGT-1" "D03_S09_AAACCTGAGTCGTACT-1" ...

I tried converting it into numeric but still the error persists which might not be related but in general do I change it to numeric or not? object$Age_at_death <- as.numeric(object$Age_at_death)