I have imported some data (30 million rows) to the quickstart VM (single node) using the following command. 

sqoop import  -Dmapreduce.map.memory.mb=1024 -Dmapreduce.map.java.opts=-Xmx7200m -Dmapreduce.task.io.sort.mb=2400 --connect jdbc:mysql://my.ip.address/perkdbdev --username root -P --hive-import --table table_name --as-parquetfile --warehouse-dir=/home/cloudera/hadoop  -m 10

It has added the data successfully, but I am facing with an issue when I issue any aggregate function statement from the Hue Query editor interface for Impala. I am getting 

argument of type 'NoneType' is not iterable

Do I need to do anything after importing the data to avoid this error ? I googled for sometime, but the only information I got is that this is some error with Python, but I am not very sure about it. I am getting the error while running the following query .

select count(id) from my_table_name;