Convert "Strand" Value from Star aligner output to "SAF" format to extract feature counts with user defined annotation

Question

[niranjanpandeshwar]

Star output "SJ.out.tab" has column 4 (column 4: strand (0: undefined, 1: +, 2: -)).

I need to use this and create my annotation file for rsubread's feature counts. A typical user defined annotation looks like the one below. I can convert the 1s and 2s into "+" and "-". How should I handle "0"?

ann <- data.frame(
GeneID=c("gene1","gene1","gene2","gene2"),
Chr="chr_dummy",
Start=c(100,1000,3000,5000),
End=c(500,1800,4000,5500),
Strand=c("+","+","-","-"),
stringsAsFactors=FALSE)
fc_SE <- featureCounts("alignResults.BAM",annot.ext=ann)