-m metabat fails with --no-zeros

[wwood]

$ cargo run -- contig -m metabat -b tests/data/issue_19_bams/*bam --no-zeros
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `target/debug/coverm contig -m metabat -b tests/data/issue_19_bams/BE_BS_R1-BE_BS_R1.reduced.bam tests/data/issue_19_bams/BE_BS_R1-BE_RX_R1.reduced.bam tests/data/issue_19_bams/BE_BS_R1-BM_ER_R7.reduced.bam tests/data/issue_19_bams/BE_BS_R1-BM_RX_R7.reduced.bam --no-zeros`
[2020-02-07T01:35:46Z INFO  coverm] CoverM version 0.3.2
[2020-02-07T01:35:46Z INFO  coverm] Using min-covered-fraction 0%
[2020-02-07T01:35:46Z INFO  coverm::contig] In sample 'BE_BS_R1-BE_BS_R1.reduced', found 365 reads mapped out of 819 total (44.57%)
[2020-02-07T01:35:46Z INFO  coverm::contig] In sample 'BE_BS_R1-BE_RX_R1.reduced', found 480 reads mapped out of 748 total (64.17%)
[2020-02-07T01:35:46Z INFO  coverm::contig] In sample 'BE_BS_R1-BM_ER_R7.reduced', found 41 reads mapped out of 219 total (18.72%)
[2020-02-07T01:35:46Z INFO  coverm::contig] In sample 'BE_BS_R1-BM_RX_R7.reduced', found 130 reads mapped out of 543 total (23.94%)
contigName	contigLen	totalAvgDepth	BE_BS_R1-BE_BS_R1.reduced.bam	BE_BS_R1-BE_BS_R1.reduced.bam-var	BE_BS_R1-BE_RX_R1.reduced.bam	BE_BS_R1-BE_RX_R1.reduced.bam-var	BE_BS_R1-BM_ER_R7.reduced.bam	BE_BS_R1-BM_ER_R7.reduced.bam-var	BE_BS_R1-BM_RX_R7.reduced.bam	BE_BS_R1-BM_RX_R7.reduced.bam-var
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /rustc/5e1a799842ba6ed4a57e91f7ab9435947482f7d8/src/libcore/macros/mod.rs:15:40
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.