public <T> @Nullable T getValue(
            final @NonNull String name,
            final @Nullable T defaultValue
    ) {
        return this.<T>getValue(name).orElse(defaultValue);
    }
Returns a flag value.
<p>
If using {@link CommandFlag.FlagMode#SINGLE}
then this returns the only value, if it has been specified. If using
{@link CommandFlag.FlagMode#REPEATABLE} then
it'll return the first value.

@param name         Flag name
@param defaultValue Default value
@param <T>          Value type
@return Stored value, or the supplied default value
cloud-core/src/main/java/org/incendo/cloud/parser/flag/FlagContext.java