Fixing #53 sometime domain cannot be known

ippisite/ippidb/models.py

@@ -252,7 +252,7 @@ class ProteinDomainComplex(models.Model):
     Protein-Domain association
     """
     protein = models.ForeignKey('Protein', models.CASCADE)
-    domain = models.ForeignKey('Domain', models.CASCADE)
+    domain = models.ForeignKey('Domain', models.CASCADE, null=True, blank=True)
     ppc_copy_nb = models.IntegerField(
         'Number of copies of the protein in the complex')