[Broker-J][SimpleLDAP] NPE is reported into broker logs when search user is specified but search password is not set

java.lang.NullPointerException: null
	at java.util.Hashtable.put(Hashtable.java:460)
	at org.apache.qpid.server.security.auth.manager.SimpleLDAPAuthenticationManagerImpl.setupSearchContext(SimpleLDAPAuthenticationManagerImpl.java:602)
	at org.apache.qpid.server.security.auth.manager.SimpleLDAPAuthenticationManagerImpl.validateInitialDirContext(SimpleLDAPAuthenticationManagerImpl.java:577)
	at org.apache.qpid.server.security.auth.manager.SimpleLDAPAuthenticationManagerImpl.validateOnCreate(SimpleLDAPAuthenticationManagerImpl.java:159)
	at org.apache.qpid.server.model.AbstractConfiguredObject$6.execute(AbstractConfiguredObject.java:879)
	at org.apache.qpid.server.model.AbstractConfiguredObject$6.execute(AbstractConfiguredObject.java:866)
	at org.apache.qpid.server.model.AbstractConfiguredObject$2.execute(AbstractConfiguredObject.java:637)
	at org.apache.qpid.server.model.AbstractConfiguredObject$2.execute(AbstractConfiguredObject.java:630)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl$TaskLoggingWrapper.execute(TaskExecutorImpl.java:248)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl.submitWrappedTask(TaskExecutorImpl.java:165)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl.submit(TaskExecutorImpl.java:153)
	at org.apache.qpid.server.model.AbstractConfiguredObject.doOnConfigThread(AbstractConfiguredObject.java:629)
	at org.apache.qpid.server.model.AbstractConfiguredObject.createAsync(AbstractConfiguredObject.java:865)
	at org.apache.qpid.server.model.AbstractConfiguredObjectTypeFactory.createAsync(AbstractConfiguredObjectTypeFactory.java:75)
	at org.apache.qpid.server.model.ConfiguredObjectFactoryImpl.createAsync(ConfiguredObjectFactoryImpl.java:145)
	at org.apache.qpid.server.model.AbstractConfiguredObject.addChildAsync(AbstractConfiguredObject.java:2111)
	at org.apache.qpid.server.model.BrokerImpl.addChildAsync(BrokerImpl.java:697)
	at org.apache.qpid.server.model.AbstractConfiguredObject$17.execute(AbstractConfiguredObject.java:2068)
	at org.apache.qpid.server.model.AbstractConfiguredObject$17.execute(AbstractConfiguredObject.java:2063)
	at org.apache.qpid.server.model.AbstractConfiguredObject$2.execute(AbstractConfiguredObject.java:637)
	at org.apache.qpid.server.model.AbstractConfiguredObject$2.execute(AbstractConfiguredObject.java:630)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl$TaskLoggingWrapper.execute(TaskExecutorImpl.java:248)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl$CallableWrapper$1.run(TaskExecutorImpl.java:320)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:360)
	at org.apache.qpid.server.configuration.updater.TaskExecutorImpl$CallableWrapper.call(TaskExecutorImpl.java:313)
	at com.google.common.util.concurrent.TrustedListenableFutureTask$TrustedFutureInterruptibleTask.runInterruptibly(TrustedListenableFutureTask.java:111)
	at com.google.common.util.concurrent.InterruptibleTask.run(InterruptibleTask.java:58)
	at com.google.common.util.concurrent.TrustedListenableFutureTask.run(TrustedListenableFutureTask.java:75)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.qpid.server.bytebuffer.QpidByteBufferFactory.lambda$null$0(QpidByteBufferFactory.java:464)
	at java.lang.Thread.run(Thread.java:748)