com.sun.jndi.ldap.LdapClient.search throws IOException when it finds its connection has closed but it may intermittently fail with a NullPointerException when the connection is closed in between the time that it confirms that it is still open and the time that it performs an operation on it.

java.lang.NullPointerException
at com.sun.jndi.ldap.LdapClient.search(LdapClient.java:528)
at com.sun.jndi.ldap.LdapCtx.doSearch(LdapCtx.java:1948)
at com.sun.jndi.ldap.LdapCtx.searchAux(LdapCtx.java:1810)
at com.sun.jndi.ldap.LdapCtx.c_search(LdapCtx.java:1735)