[Java] Replace `if` with `?` in Generated `toIndentedString`-methods … #1467

Job	Run time
Build Java Client JDK11 (samples/client/echo_api/java/feign-gson)	1m 19s
Build Java Client JDK11 (samples/client/echo_api/java/resttemplate)	1m 23s
Build Java Client JDK11 (samples/client/echo_api/java/resteasy)	1m 24s
Build Java Client JDK11 (samples/client/echo_api/java/apache-httpclient)	1m 47s
Build Java Client JDK11 (samples/client/echo_api/java/native)	1m 41s
	7m 34s

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