[BUG]salt.loaded.int.pillar.salthiera.__virtual__() is wrongly returning `None`. It should either return `True`, `False` or a new name. If you're the developer of the module 'salthiera', please fix this.

Description
salt-master version 3000.2 don't support salthiera

Steps to Reproduce the behavior

2020-05-07 13:39:08,123 [salt.loader      :1897][ERROR   ][11457] Exception raised when processing __virtual__ function for salt.loaded.int.pillar.salthiera. Module will not be loaded: 'module' object has no at
tribute 'which'
2020-05-07 13:39:08,124 [salt.loader      :1913][WARNING ][11457] salt.loaded.int.pillar.salthiera.__virtual__() is wrongly returning `None`. It should either return `True`, `False` or a new name. If you're the
 developer of the module 'salthiera', please fix this.
2020-05-07 13:39:09,361 [salt.pillar      :976 ][CRITICAL][11457] Specified ext_pillar interface salthiera is unavailable
2020-05-07 13:39:09,513 [salt.loader      :1897][ERROR   ][11453] Exception raised when processing __virtual__ function for salt.loaded.int.pillar.salthiera. Module will not be loaded: 'module' object has no at
tribute 'which'
2020-05-07 13:39:09,513 [salt.loader      :1913][WARNING ][11453] salt.loaded.int.pillar.salthiera.__virtual__() is wrongly returning `None`. It should either return `True`, `False` or a new name. If you're the
 developer of the module 'salthiera', please fix this.

Expected behavior

Screenshots

Versions Report

!156 # salt --versions-report
Salt Version:
           Salt: 3000.2
 
Dependency Versions:
           cffi: 1.6.0
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.7.2
        libgit2: 0.26.3
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: 2.14
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: 0.26.4
         Python: 2.7.5 (default, Aug  7 2019, 00:51:29)
   python-gnupg: Not Installed
         PyYAML: 3.10
          PyZMQ: 15.3.0
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.1.4
 
System Versions:
           dist: centos 7.6.1810 Core
         locale: UTF-8
        machine: x86_64
        release: 3.10.0-957.12.2.el7.x86_64
         system: Linux
        version: CentOS Linux 7.6.1810 Core

Additional context
Add any other context about the problem here.

Locate the salthiera external pillar entry point and its virtual function, then reproduce the loader error with the supplied Salt 3000.2 environment details. Verify completion by confirming the module loads and the salthiera external pillar is no longer reported unavailable.