NullPointer when trying to set LP output

Command:

flux-capacitor -i bamfile -a annotation_file -o ouptut --threads nthreads

Output:

[PROFILE] Scanning the input and getting the attributes.

profiling OK (00:23:52)

first round finished .. took 1432 sec.

12325 single transcript loci

377309560 mappings in file

43276718 mappings fall in single transcript loci

4615251872 mappings in annotation-mapped pairs

81,121 min/max read length

[SOLVE] Deconvolving reads of overlapping transcripts.

decomposing [WARN] Fraction inconsistency FBtr0077393.27.homologue -2.304722170272954

...

[ERROR] Failed to set lp output to:
null
java.lang.NullPointerException
at java.io.FileOutputStream.<init>(FileOutputStream.java:206)
at java.io.FileOutputStream.<init>(FileOutputStream.java:136)
at barna.flux.capacitor.reconstruction.GraphLPsolver.run(GraphLPsolver.java:950)
at barna.flux.capacitor.reconstruction.FluxCapacitor$LocusSolver.call(FluxCapacitor.java:1097)
at barna.flux.capacitor.reconstruction.FluxCapacitor.explore(FluxCapacitor.java:2631)
at barna.flux.capacitor.reconstruction.FluxCapacitor.call(FluxCapacitor.java:1886)
at barna.flux.capacitor.reconstruction.FluxCapacitor.call(FluxCapacitor.java:74)
at barna.commons.launcher.Flux.main(Flux.java:198)

unusual normalization factor: 0.03384014257154664
[WARN] Unsolved system: 2L:4891851-4941363W
[WARN] Fraction inconsistency FBtr0302984.1.homologue -2.313103458721854
Model name: FBtr0080341.1.homologue