Handling null values in Map keys - cassandra

Question

I am using cassandra 3.10 and in order to use a Group by function on non primary partitions I am referring: http://www.batey.info/cassandra-aggregates-min-max-avg-group.html, which is using map keys to do the same. When I execute select group_and_total(name,count) from school; and I get the error ServerError: java.lang.NullPointerException: Map keys cannot be null.
The problem is that name column has some null values in it and is there any way by modifying the function and getting the desired result instead of removing the rows that have null values in it.
The schema of the table is
Table school{
name text,
count int,
roll_no text,
...
primary key(roll_no)
}
The functions that I am using for Group by are:
CREATE FUNCTION state_group_and_total( state map<text, int>, type text, amount int )
CALLED ON NULL INPUT
RETURNS map<text, int>
LANGUAGE java AS '
Integer count = (Integer) state.get(type); if (count == null) count = amount; else count = count + amount; state.put(type, count); return state; ' ;
CREATE OR REPLACE AGGREGATE group_and_total(text, int)
SFUNC state_group_and_total
STYPE map<text, int>
INITCOND {};

Answer 1

Schema that you mentioned
CREATE TABLE temp.school (
roll_no text PRIMARY KEY,
count int,
name text
)
Sample inputs into the table
roll_no | count | name
---------+-------+------
6 | 1 | b
7 | 1 | null
4 | 1 | b
3 | 1 | a
5 | 1 | b
2 | 1 | a
1 | 1 | a
(7 rows)
Note: There is one null value in the name column.
Modified Function definition
CREATE FUNCTION temp.state_group_and_total(state map<text, int>, type text, amount int)
RETURNS NULL ON NULL INPUT
RETURNS map<text, int>
LANGUAGE java
AS $$Integer count = (Integer) state.get(type);if (count == null) count = amount;else count = count + amount;state.put(type, count); return state;$$;
Note: removed CALLED ON NULL INPUT and added RETURNS NULL ON NULL INPUT
Aggregate definition:
CREATE AGGREGATE temp.group_and_total(text, int)
SFUNC state_group_and_total
STYPE map<text, int>
INITCOND {};
Query output:
cassandra#cqlsh:temp> select group_and_total(name,count) from school;
temp.group_and_total(name, count)
-----------------------------------
{'a': 3, 'b': 3}
(1 rows)