Appion

add check since only one of these flags should exist

runJob.py ctffind4.py --ampcontrast=0.07 --fieldsize=1024 --resmin=50 --resmax=10 --defstep=0.1 --numstep=25 --dast=0.05 --bestdb --nominal= --parallel --runname=ctffind4run7 --rundir=/data/appion/20160706-LC-SM-minicells-tomo/ctf/ctffind4run7 --commit --preset=k2tomo_12K --projectid=1 --session=20160706-LC-SM-minicells-tomo --no-rejects --no-wait --no-continue --expid=102 --jobtype=ctfestimate --ppn=1 --nodes=1 --walltime=240 --jobid=898

$ cat ctffind4run7.appionsub.log
... Time stamp: 16jul18s13
... Function name: ctffind4
... Appion directory: /usr/lib/python2.6/site-packages
Usage: ctffind4.py --projectid=## --runname=<runname> --session=<session> --preset=<preset> --description='<text>' --commit [options]

ctffind4.py: error: option --nominal: invalid floating-point value: ''

the parameter check in appion/bin/ctffind4.py has no default value.