Prior to this commit, MutablePropertySources#get(String) would throw
IndexArrayOutOfBoundsException if the named property source does not
actually exist. This is a violation of the PropertySource#get contract
as described in its Javadoc.
The implementation now correctly checks for the existence of the named
property source, returning null if non-existent and otherwise returning
the associated PropertySource.
Other changes
- Rename PropertySourcesTests => MutablePropertySourcesTests
- Polish MutablePropertySourcesTests for style, formatting
- Refactor MutablePropertySources for consistency
Issue: SPR-9185
Backport-Issue: SPR-9179
Backport-Commit: 15d1d824b5
7d72ab59ae