Fix possible NPE if user code creates a REST client 'early' #6901

Job	Run time
build	5m 45s
checkstyle	3m 52s
copyright	3m 29s
shellcheck	3m 9s
tests/tck-cdi	17m 17s
tests/native-image-mp-1-linux	6m 44s
tests/core	11m 8s
tests/tck-rest	15m 14s
tests/native-image-mp-2-linux	12m 40s
spotbugs/core	10m 59s
tests/it	14m 41s
tests/tck-others	16m 53s
spotbugs/integrations	7m 16s
tests/native-image-mp-3-linux	6m 49s
tests/dbclient	9m 4s
tests/native-image-se-1-linux	7m 0s
spotbugs/others	12m 48s
archetypes/r1-jar	6m 42s
tests/dbclient-oracle	16m 14s
tests/native-image-inject-linux	6m 24s
tests/others	12m 38s
archetypes/r2-jar	6m 49s
tests/native-image-mp-1-macos	9m 58s
docs	4m 57s
archetypes/r3-jar	6m 18s
tests/native-image-mp-2-macos	20m 0s
examples/linux	10m 11s
archetypes/r4-jar	6m 42s
javadoc (core)	7m 0s
tests/native-image-mp-3-macos	9m 43s
examples/macos	10m 42s
archetypes/r5-jar	5m 12s
tests/native-image-se-1-macos	9m 0s
javadoc (integrations)	5m 22s
tests/native-image-inject-macos	7m 29s
javadoc (others)	7m 54s
archetypes/legacy	4m 32s
tests/packaging-jar-linux	8m 44s
tests/packaging-jlink-linux	8m 50s
quickstarts/linux	11m 42s
tests/packaging-jar-macos	5m 15s
quickstarts/macos	19m 37s
tests/packaging-jlink-macos	7m 11s
tests/results	14s
gate	1s
	6h 40m 9s

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