MP-config extension fails for empty values

[pa314159]

jersey/ext/microprofile/mp-config/src/main/java/org/glassfish/jersey/microprofile/config/ConfigurationModel.java

Line 86 in 741aad4

config.getPropertyNames().forEach(c -> properties.put(c, config.getValue(c, String.class)));

This line may fail if the value of the configuration is empty.

E.g. systems may set environment variables like this

export AN_EMPTY_VARIABLE=

MP-config trims all empty values to null so the invocation of

config.getValue("AN_EMPTY_VARIABLE", String.class)

fails with NoSuchElementException

[senivam]

For the record:
MP-config empty properties handling behavior changed since MP config 2.0. Changes are described here: eclipse/microprofile-config#446
Following PR introduced changes to code: https://github.com/eclipse/microprofile-config/pull/598/files

for us this means that we shall handle external configs' properties handling more carefully.

Internal Jersey properties handling works without changes.