Fix PHP 7.4 bug #159

[mstralka]

Sorry for the reformatting this was really only a few changes to fix #159 by changing several instances of:

if ($this->tenantTokens[$tenantKey] == null) {

to

if (!isset($this->tenantTokens[$tenantKey]) || $this->tenantTokens[$tenantKey] == null) {

and initializing $this->tenantTokens in the constructor instead of a local variable.