fix null pointer exception

Introduction:

Storage service is giving 500s due to null pointer exception when trying to convert ACL viewers into an array list but we dont have any such log for same. Also it is not reproducible because we never ingest a record with acl fields empty. Hence we want to log the statement if ACL is empty and throw a NPE with proper reasoning.

Exception:

org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)| at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)| at org.apache.tomcat.util.threads.ThreadPoolExecutorWorker.run(ThreadPoolExecutor.java:659)| at org.apache.tomcat.util.threads.TaskThreadWrappingRunnable.run(TaskThread.java:61)| at java.lang.Thread.run(Thread.java:750)|Caused by: java.lang.NullPointerException| at org.opengroup.osdu.storage.provider.azure.CloudStorageImpl.**hasViewerAccessToRecord(CloudStorageImpl.java:238)**| at org.opengroup.osdu.storage.provider.azure.CloudStorageImpl.read(CloudStorageImpl.java:284)| at org.opengroup.osdu.storage.provider.azure.CloudStorageImplFastClassBySpringCGLIB47bbc639.invoke()| at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)| at

ref #151 (closed)