salt: Continuous error in the proxy minion logs

Description of Issue/Question

For many devices, I see this error continuously appearing in the minion proxy logs: Exception argument of type ‘bool’ is not iterable occurred in scheduled job

I am using a elastic search returner for all salt logs and it is getting clogged with this same message too many times.

It happens with both Cisco and Juniper device. Any idea what could be the issue?

Setup

Pillar file is pretty simple:

proxy:
  proxytype: napalm
  driver: ios
  host: 1.2.4.5
  username: *****
  password: *****

Steps to Reproduce Issue

Log:

[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[DEBUG   ] Sending global request "keepalive@lag.net"
[DEBUG   ] Global request denied.
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[DEBUG   ] Sending global request "keepalive@lag.net"
[DEBUG   ] Global request denied.
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job
[ERROR   ] Exception argument of type 'bool' is not iterable occurred in scheduled job

Versions Report

Salt Version:
           Salt: 2018.3.0

Dependency Versions:
           cffi: 1.11.5
       cherrypy: Not Installed
       dateutil: 2.4.2
      docker-py: Not Installed
          gitdb: 0.6.4
      gitpython: 1.0.1
          ioflo: Not Installed
         Jinja2: 2.8
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: 1.0.3
   msgpack-pure: Not Installed
 msgpack-python: 0.4.6
   mysql-python: Not Installed
      pycparser: 2.18
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 2.7.12 (default, Dec  4 2017, 14:50:18)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 15.2.0
           RAET: Not Installed
          smmap: 0.9.0
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4

System Versions:
           dist: Ubuntu 16.04 xenial
         locale: UTF-8
        machine: x86_64
        release: 4.4.0-116-generic
         system: Linux
        version: Ubuntu 16.04 xenial