NPE thrown by ABS

Input data :
-file 'a' starts-
A|1
B|2

-file 'a' ends-
(Note the empty line at the end)

The following script does not work.
a = load 'a' using PigStorage('|') as (x:chararray, y:double);
b = foreach a generate *, ABS(y - 2*y) as test;
dump b;

The function ABS throws a NPE instead of giving out a null for the last line in the input:
java.lang.NullPointerException
at org.apache.pig.builtin.DoubleAbs.exec(DoubleAbs.java:45)
at org.apache.pig.builtin.DoubleAbs.exec(DoubleAbs.java:28)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:216)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:281)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.getNext(PhysicalOperator.java:324)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.processPlan(POForEach.java:332)
at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.getNext(POForEach.java:284)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.runPipeline(PigMapBase.java:261)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.map(PigMapBase.java:256)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.map(PigMapBase.java:58)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:621)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
at org.apache.hadoop.mapred.Child.main(Child.java:170)