I am using Hibernate OGM 5.0.1 with MongoDB 3.2.6. My JPA QL is below:
String checkquery = "SELECT p FROM pppoe_test p where p.sourceIP=:source_ip and p.login>:logentrytime and (p.logout>:logentrytime OR p.logout IS NULL)";

I get an error like:
no viable alternative at input 'NULL'
HQL000002: The query SELECT p FROM PPPoESession p where p.sourceIP=:source_ip and p.login>:logentrytime and (p.logout>:logentrytime OR p.logout IS NULL) is not valid

Exception in thread "main" org.hibernate.hql.ParsingException: HQL000002: The query SELECT p FROM PPPoESession p where p.sourceIP=:source_ip and p.login>:logentrytime and p.logout>:logentrytime OR p.logout IS NULL is not valid; Parser error messages: [[statement, statementElement, selectStatement, queryExpression, querySpec, whereClause, logicalExpression, expression, logicalOrExpression, logicalAndExpression, negatedExpression, equalityExpression]: line 1:144 state 0 (decision=51) no viable alt; token=[@51,144:147='NULL',<75>,1:144]].
at org.hibernate.hql.QueryParser.parseQuery(QueryParser.java:70)
at org.hibernate.ogm.datastore.mongodb.query.parsing.impl.MongoDBBasedQueryParserService.parseQuery(MongoDBBasedQueryParserService.java:40)
at org.hibernate.ogm.query.impl.OgmQueryTranslator.getQuery(OgmQueryTranslator.java:169)
at org.hibernate.ogm.query.impl.OgmQueryTranslator.getLoader(OgmQueryTranslator.java:134)
at org.hibernate.ogm.query.impl.OgmQueryTranslator.list(OgmQueryTranslator.java:128)
at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:216)
at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1326)
at org.hibernate.internal.QueryImpl.list(QueryImpl.java:87)
at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:606)
at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:483)

Here is the mongodb doc, that I had earlier inserted via the OGM.

I do have the attributes setup properly in the entity

@Entity (name="pppoe_test")
public class PPPoESession { ...

@Temporal(TemporalType.TIMESTAMP)
private Date logout;

@Basic(optional = false)
private String user;

@Basic(optional = false)
private String sourceIP;