public default <Type> Collection<Type> getRequiredPropertyCollection(
            GuacamoleProperty<Type> property) throws GuacamoleException {
        return new DefaultEnvironment(this).getRequiredPropertyCollection(property);
    }
Given a GuacamoleProperty, parses and returns a sorted Collection of
values for that property in guacamole.properties. An exception is thrown
if the value is not provided. The implementation of parsing and returning
a collection of multiple values is up to the individual property
implementations, and not all implementations will support reading and
returning multiple values.

@param <Type>
    The type that the given property is parsed into.

@param property
    The property to read from guacamole.properties.

@return
    A sorted Collection of the property as read from guacamole.properties.

@throws GuacamoleException 
    If an error occurs while parsing the value for the given property in
    guacamole.properties, or if the property is not specified.
guacamole-ext/src/main/java/org/apache/guacamole/environment/Environment.java