As an alternative, this method creates a BooleanProp which is true if the key exists in the map and is not assigned a value other than "true", compared case-insensitively, or the empty string. This way -Dmy.property results in a true-valued property, but -Dmy.property=false does not.
A BooleanProp with a liberal truth policy
The java definition of property truth is that the key be in the map and the value be equal to the String "true", case insensitively. This method creates a BooleanProp instance which adheres to that definition.
A BooleanProp which acts like java's Boolean.getBoolean