GenericDateJdbcType fails to read a null Duration

[andrezimmermann]

After upgrading 0.15.0-RC to 0.15.2, some columns mapped as Option[Duration] started to fail when selecting from DB.
It fails at this line 43 of GenericDateJdbcType

Below the exception.

[info]   org.postgresql.util.PSQLException: Failed to create object for: interval.
[info]   at org.postgresql.jdbc.PgConnection.getObject(PgConnection.java:586)
[info]   at org.postgresql.jdbc.PgResultSet.getObject(PgResultSet.java:3360)
[info]   at com.github.tminglei.slickpg.date.PgDateJdbcTypes$GenericDateJdbcType.getValue(PgDateJdbcTypes.scala:43)
[info]   at slick.jdbc.SpecializedJdbcResultConverter$$anon$2.read(SpecializedJdbcResultConverters.scala:45)
[info]   at slick.jdbc.SpecializedJdbcResultConverter$$anon$2.read(SpecializedJdbcResultConverters.scala:43)
[info]   at slick.relational.ProductResultConverter.read(ResultConverter.scala:53)
[info]   at slick.relational.ProductResultConverter.read(ResultConverter.scala:43)
[info]   at slick.relational.TypeMappingResultConverter.read(ResultConverter.scala:133)
[info]   at slick.jdbc.JdbcInvokerComponent$QueryInvokerImpl.extractValue(JdbcInvokerComponent.scala:36)
[info]   at slick.jdbc.StatementInvoker$$anon$1.extractValue(StatementInvoker.scala:66)
[info]   ...
[info]   Cause: java.lang.NullPointerException:
[info]   at org.postgresql.util.PGInterval.setValue(PGInterval.java:80)
[info]   at org.postgresql.jdbc.PgConnection.getObject(PgConnection.java:571)
[info]   at org.postgresql.jdbc.PgResultSet.getObject(PgResultSet.java:3360)
[info]   at com.github.tminglei.slickpg.date.PgDateJdbcTypes$GenericDateJdbcType.getValue(PgDateJdbcTypes.scala:43)
[info]   at slick.jdbc.SpecializedJdbcResultConverter$$anon$2.read(SpecializedJdbcResultConverters.scala:45)
[info]   at slick.jdbc.SpecializedJdbcResultConverter$$anon$2.read(SpecializedJdbcResultConverters.scala:43)
[info]   at slick.relational.ProductResultConverter.read(ResultConverter.scala:53)
[info]   at slick.relational.ProductResultConverter.read(ResultConverter.scala:43)
[info]   at slick.relational.TypeMappingResultConverter.read(ResultConverter.scala:133)
[info]   at slick.jdbc.JdbcInvokerComponent$QueryInvokerImpl.extractValue(JdbcInvokerComponent.scala:36)