Fix NPE #232

Job	Run time
Build DSE 6.8 (jdk8) Ubuntu Docker image	2m 37s
Build DSE 6.8 (jdk8) Ubuntu Docker image	2m 44s
Build DSE 6.8 (jdk11) Ubuntu Docker image	3m 23s
Build DSE 6.8 (jdk11) Ubuntu Docker image	4m 16s
Build 3.11 Cassandra Docker image	3m 16s
Build 4.0 Cassandra Docker image	3m 21s
Build 4.0 Cassandra Docker image	1m 44s
Build 4.1 Cassandra Docker image	3m 39s
Build 4.1 Cassandra Docker image	2m 1s
Build 3.11-ubi8 Cassandra Docker image	2m 51s
Build 4.0-ubi8 Cassandra Docker image	2m 57s
Build 4.1-ubi8 Cassandra Docker image	2m 35s
Build 3.11 Cassandra Docker image	2m 3s
Build 3.11-ubi8 Cassandra Docker image	2m 14s
Build 4.0-ubi8 Cassandra Docker image	2m 21s
Build 4.1-ubi8 Cassandra Docker image	2m 29s
	44m 31s

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