I am trying to find discrete log over $GF(P)$ using Cado-NFS (https://gitlab.inria.fr/cado-nfs/cado-nfs/-/blob/master/README.dlp). It works well for random primes. But if I take primes that are divisor of numbers of the form $2^n-1$ for some positive integer $n$, it gives error. I use this in terminal:

```
./cado-nfs.py -dlp -ell factor of P-1 target=a P
```

I am getting error as follows:

```
Traceback (most recent call last):
File "Prime_5.sage.py", line 245, in <module>
y = DLP(a,b, PRIME_FACTORS[j]) #gp.znlog(a, gp.Mod(b, PRIME_FACTORS[j])) #DLP(a,b, PRIME_FACTORS[j])
File "Prime_5.sage.py", line 90, in DLP
w = NFS(y,x,z)
File "Prime_5.sage.py", line 28, in NFS
x1 = ZZ(x1)
File "sage/structure/parent.pyx", line 898, in sage.structure.parent.Parent.__call__ (build/cythonized/sage/structure/parent.c:9339)
File "sage/structure/coerce_maps.pyx", line 161, in sage.structure.coerce_maps.DefaultConvertMap_unique._call_ (build/cythonized/sage/structure/coerce_maps.c:4628)
File "sage/structure/coerce_maps.pyx", line 156, in sage.structure.coerce_maps.DefaultConvertMap_unique._call_ (build/cythonized/sage/structure/coerce_maps.c:4520)
File "sage/rings/integer.pyx", line 713, in sage.rings.integer.Integer.__init__ (build/cythonized/sage/rings/integer.c:6568)
File "sage/rings/integer.pyx", line 7097, in sage.rings.integer.mpz_set_str_python (build/cythonized/sage/rings/integer.c:43422)
TypeError: unable to convert '' to an integer
```