@Override
    public final OptionalBoolean getAsBoolean(String key) {
        final BooleanProperty prop = (BooleanProperty) properties.get(key);
        if (prop == null) {
            return OptionalBoolean.empty();
        } else {
            return OptionalBoolean.ofNullable(prop.getValue());
        }
    }
{@inheritDoc}
@deprecated Not supported for observables
tool-parent/tool-config/src/main/java/com/speedment/tool/config/AbstractDocumentProperty.java