Value 'empty' in metadata files for 'tokens' property cause problems in plugins

[romani]

https://checkstyle.org/config_misc.html#DescendantToken_Properties
https://checkstyle.org/config_coding.html#IllegalTokenText_Properties

example:

but in meta it is:

checkstyle/src/main/resources/com/puppycrawl/tools/checkstyle/meta/checks/DescendantTokenCheck.xml

Lines 49 to 51 in 58bae0f

	<property default-value="empty" name="tokens" type="anyTokenTypesSet">
	<description>tokens to check</description>
	</property>

checkstyle/src/main/resources/com/puppycrawl/tools/checkstyle/meta/checks/coding/IllegalTokenTextCheck.xml

Lines 25 to 28 in 58bae0f

	<property default-value=""
	name="tokens"
	type="java.lang.String[]"
	validation-type="tokenSet">

both this Checks have empty tokens property, in WEB documentation we cannot render empty value, so we put empty word. But in metadata and javadoc we should be strict and be more technical, so value should be empty string value.

such problem in metadata caused problems described at checkstyle/sonar-checkstyle#338 (comment)

[romani]

Fix is merged