[app][process] fix default value

est/app/process.py

@@ -77,7 +77,7 @@ def main(argv):
         "--input-dimensions",
         "--dimensions",
         dest="input_dimensions",
-        default="None",
+        default=None,
         help="dimension of the input as (Z,Y,X) for example."
         "If None will take default unit according to the input type",
     )
@@ -86,28 +86,28 @@ def main(argv):
         "--input-I0",
         "--I0",
         dest="input_I0",
-        default="None",
+        default=None,
         help="url to I0",
     )
     parser.add_argument(
         "--input-I1",
         "--I1",
         dest="input_I1",
-        default="None",
+        default=None,
         help="url to I1",
     )
     parser.add_argument(
         "--input-I2",
         "--I2",
         dest="input_I2",
-        default="None",
+        default=None,
         help="url to I2",
     )
     parser.add_argument(
         "--input-mu-ref",
         "--mu-ref",
         dest="input_mu_ref",
-        default="None",
+        default=None,
         help="url to mu_ref",
     )
     # spec file specific inputs