Check for '?' in Strand.set_sequence()

mrdna/segmentmodel.py

@@ -781,7 +781,7 @@ class Segment(ConnectableElement, Group):
             else:
                 assert(len(self.sequence) == self.num_nt) # TODO move
                 for i in range(len(self.sequence)):
-                    if self.sequence[i] is None:
+                    if self.sequence[i] in (None,'?'):
                         self.sequence[i] = 'T'
         else:
             raise ValueError("'fill_sequence' parameter must be one of 'random' 'A' 'T' 'C' or 'G'.")