update for when grad_dev is not defined

Author: mattfeld

nipype/interfaces/fsl/dti.py

@@ -349,9 +349,10 @@ def _run_interface(self, runtime):
                  os.path.join(subjectdir, 'bvals'))
         copyfile(self.inputs.bvecs,
                  os.path.join(subjectdir, 'bvecs'))
-        _, _, ext = split_filename(self.inputs.grad_dev)
-        copyfile(self.inputs.grad_dev,
-                 os.path.join(subjectdir, 'grad_dev' + ext))
+        if isdefined(self.inputs.grad_dev):
+            _, _, ext = split_filename(self.inputs.grad_dev)
+            copyfile(self.inputs.grad_dev,
+                     os.path.join(subjectdir, 'grad_dev' + ext))
 
         retval = super(BEDPOSTX5, self)._run_interface(runtime)