Clarification of config.getValue() for an Optional

[Joseph-Cass]

Description
Should config.getValue("int.missing.key", OptionalInt.class) throw a NoSuchElementException according to this bit of spec? (where int.missing.key is not defined in a config source)

microprofile-config/api/src/main/java/org/eclipse/microprofile/config/Config.java

Lines 130 to 131 in 03c6f05

	* @throws java.util.NoSuchElementException
	* if the property is not defined or is defined as an empty string or the converter returns {@code null}

If yes, It seems like this could be a relatively common mistake, which suggests to me it may be worth having a TCK for (If there isn't one already- I couldn't find one)

[Emily-Jiang]

Good observation! This was an oversight when adding OptionalInt, OptionalDouble, OptionalLong. Effectively, when the type is Optionalxxx, the getValue will return an Optionalxxx. If we throw NoSuchElementException, this defeats the purpose of Optionalxxx. With this, I suggest to update javadoc to not to throw this exception if the class type is Optionalxxx. What others think?

[radcortez]

A related case that we may also want to clarify is when you call getOptionalValue("property", Optional*.class). Right now in SR Config, we just return a Optional<Optional*>, which I think it is ok. Some may expect this to be flattened.