public Set<String> getChoices() {
        return choices;
    }
Returns the (immutable) set of choices for the values of this property.
Only defined for {@link ValueType#OPEN_CHOICE open} and
{@link ValueType#CLOSED_CHOICE closed choice} value types.

@return available choices, or <code>null</code>
tika-core/src/main/java/org/apache/tika/metadata/Property.java