adapt ConfigOptionProvider javadoc to reality

...as several implementations return null. Also, it does not make
much sense to instantiate empty collections all the time, as the
majority of call will be returned with no results.

Signed-off-by: Simon Kaufmann <simon.kfm@googlemail.com>

bundles/config/org.eclipse.smarthome.config.core/src/main/java/org/eclipse/smarthome/config/core/ConfigOptionProvider.java

@@ -28,8 +28,7 @@ public interface ConfigOptionProvider {
      *            the parameter name for which the requested options shall be returned
      * @param locale
      *            locale
-     * @return the configuration options provided by this provider (not
-     *         null, could be empty)
+     * @return the configuration options provided by this provider if any (may be null)
      */
     Collection<ParameterOption> getParameterOptions(URI uri, String param, Locale locale);
 }