I'm trying to follow tutorial on pulse simulation described in qiskit.org.
The generated PulseQobj is well executed with AER simulator, but it throws JSONDecodeError when using real backends (ex. ibmq-armonk). The PulseQobj passed the validation (```validate_qobj_against_schema```), so I'm struggling to find the reason. Qobj, generated by ```QuantumCircuit``` command, does not raise this error.

I connected to real device with APItoken, and qiskit version is up to date (qiskit 0.22.0).
Below is the trial code with real device, and log after backend.run(PulseQobj)
```
%matplotlib inline

import numpy as np
from qiskit.ignis.characterization.calibrations import rabi_schedules, RabiFitter
from qiskit.pulse import DriveChannel
from qiskit.compiler import assemble
from qiskit.qobj.utils import MeasLevel, MeasReturnType
from qiskit import IBMQ

IBMQ.enable_account(APItoken, proxies = ProxyConfig, verify = certPath)
provider = IBMQ.get_provider(hub=hub, group=group, project=project)
backend = provider.get_backend(device)

# qubit list
qubits = [0]

# drive amplitudes to use
num_exps = 64
drive_amps = np.linspace(0, 1.0, num_exps)

# drive shape parameters
drive_duration = 2048
drive_sigma = 256

# list of drive channels
drive_channels = [DriveChannel(0)]

# construct the schedules
rabi_schedules, xdata = rabi_schedules(amp_list=drive_amps, 
                                       qubits=qubits, 
                                       pulse_width=drive_duration, 
                                       pulse_sigma=drive_sigma,
                                       drives=drive_channels, 
                                       inst_map=backend.defaults().instruction_schedule_map, 
                                       meas_map=backend.configuration().meas_map)

rabi_qobj = assemble(rabi_schedules, 
                     backend=backend,
                     meas_level=1, 
                     meas_return='avg',
                     shots=512)

result = backend.run(rabi_qobj).result()

```

    ---------------------------------------------------------------------------
    JSONDecodeError                           Traceback (most recent call last)
    <ipython-input-17-16f293a93614> in <module>
    ----> 1 arm_result = backend.run(rabi_qobj).result()
    
    JSONDecodeError: Expecting value: line 1 column 1 (char 0)