Allow empty parameters strings

[rrg92]

When using the script with in some situations, we dont have control over the values passed to arguments (e.g: zabbix user parameters. If user pass a empty parameter, zabbix will expand to empty string).

If this cases, the script will report a error. With this enhacement, user now can specify a flag on option definition (doc or via array):

--myOption=*

In this case, the scirpt will not raise error if user passes a empty string;