Read through fails to read rows with NULL values

[shkediy]

If a row in the database contains a null value for some column that does not have not-null property set to true (meaning that it can have a null value), read through fails to read that row.
to reproduce, insert a row that have a null value for some property, then try "hgetall ".
The command returns:
(empty array)

The RG.GETEXUCUTION output show:

1. 1. "shard_id"
   2. "0000000000000000000000000000000000000144"
   3. "execution_plan"
   4. 1. "status"
      2. "done"
      3. "shards_received"
      4. (integer) 0
      5. "shards_completed"
      6. (integer) 0
      7. "results"
      8. (integer) 0
      9. "errors"
   5. 1. "java.lang.NullPointerException|\tat com.redislabs.PropertyData.convertToStr(PropertyData.java:64)|\tat com.redislabs.ReadSource.foreach(ReadSource.java:87)|\tat com.redislabs.ReadSource.foreach(ReadSource.java:18)|"
   6. "total_duration"
   7. (integer) 1221
   8. "read_duration"
   9. (integer) 0
   10. "steps"
   11. 1. 1. "type"
          2. "foreach"
          3. "duration"
          4. (integer) 0
          5. "name"
          6. "JVM_Foreach"
          7. "arg"
          8. "java object"
       2. 1. "type"
          2. "map"
          3. "duration"
          4. (integer) 0
          5. "name"
          6. "JVM_ToJavaRecordMapper"
          7. "arg"
          8. ""

It looks like it throws an exception when trying to convert the null value to string. It should ignore a null value.