Enable zero rep delay #2 (Qiskit#5129)

* Enable zero rep delay

* Add backend fix

Co-authored-by: Luciano Bello <luciano.bello@ibm.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/providers/models/backendconfiguration.py

@@ -270,7 +270,7 @@ def __init__(self, backend_name, backend_version, n_qubits,
         self.dynamic_reprate_enabled = dynamic_reprate_enabled
         if rep_delay_range:
             self.rep_delay_range = [_rd * 1e-6 for _rd in rep_delay_range]  # convert to sec
-        if default_rep_delay:
+        if default_rep_delay is not None:
             self.default_rep_delay = default_rep_delay * 1e-6   # convert to sec
 
         # max_experiments must be >=1