bam2FastQ generates empty fastq files

[LanyingMa]

Hi, i recently use bamUtil to extract reads to be paried-read fastq files from bam file. They found read pairs but the generated fastq files are empty.
bam bam2FastQ --in in_file.bam --firstOut in_file_r1.fastq --secondOut in_file_r2.fastq
When it is done running, it says:

Found 80109518 read pairs.
Found 0 unpaired reads.

but the two fastq files are empty with size as 0.. Could you please help me out on it? Thank you