Error convolving Herschel filter

I've recently started to try to use the python version of the sed fitting tool, and I need to add herschel and Atlasgal filters.

I've tried to follow the documents and the issues raised in the sedfitter github page. But i've hit a roadblock.

What i'm using is his:

__________________________________________________
```
from sedfitter.filter import Filter
from sedfitter.convolve import convolve_model_dir
from astropy import units as u

hersh_pacs_70 = Filter()
hersh_pacs_70.name = 'pacs70'
hersh_pacs_70.central_wavelength = 71.330763 * u.micron
hersh_pacs_70.read('Herschel_Pacs.blue_mic.dat')

model_dir = '../models_sed_fit/models_r06'
convolve_model_dir(model_dir, [hersh_pacs_70])
```
_________________________________________________

I took the Hershel transmission curve from the Virtual observatory, converted the wavelenghts into microns, ordered from bigger wavelength to lower and added the #wave to the header. The Herschel file is something like this:

>
> \# wav = 71.330763
> 118.69400024000001 1.06E-4
> 118.34300232 1.11E-4
> 117.9940033 1.15E-4

Unfortunately when i run the script I end up with the following error:

```
python new_convolve.py
INFO: 200710 SEDs found in /home/gteixeira/models_sed_fit/models_r06 [sedfitter.convolve.convolve]
|>-----------------------------------------| 0 /200k ( 0.00%)INFO: Rebinning filters [sedfitter.convolve.convolve]
Traceback (most recent call last):
File "new_convolve.py", line 53, in
convolve_model_dir(model_dir, [hersh_pacs_70])
File "/usr/lib/python2.7/site-packages/sedfitter/convolve/convolve.py", line 41, in convolve_model_dir
return _convolve_model_dir_1(model_dir, filters, overwrite=overwrite)
File "/usr/lib/python2.7/site-packages/sedfitter/convolve/convolve.py", line 100, in _convolve_model_dir_1
binned_filters = [f.rebin(s.nu) for f in filters]
File "/usr/lib/python2.7/site-packages/sedfitter/filter/filter.py", line 107, in rebin
self_nu_hz = self.nu.to(u.Hz).value
AttributeError: 'NoneType' object has no attribute 'to'
```

Do you know what I'm missing? Do I still need to define nu despite reading the transmission from the file?

Start at sedfitter/filter/filter.py in rebin and follow the call from sedfitter/convolve/convolve.py:100 using the Filter setup shown in the issue. Reproduce the NoneType failure with the Herschel transmission file, determine how read populates the filter data, and add a focused regression test showing that convolve_model_dir handles this input without the error.

Written by the indexing model from the issue text.