Error Cannot call method "substring" of null in Script Values - PDI - pentaho

Question

I'm using the PDI Spoon and wrote this script in Script Values to get values, check and transform:
var cte;
cte = gera_cte (CTRC.getString(), Numero_CTe.getString());
function gera_cte (arg1, arg2)
{
if (arg2 == 0) {
return arg1.substring(3,9);
}
else
{
return arg2.substring(4,10);
}
}
But when the script read the last record, this happen:
2016/02/05 17:28:40 - Gera Num Cte.0 - ERROR (version 5.0.1-stable, build 1 from 2013-11-15_16-08-58 by buildguy) : Erro inesperado
2016/02/05 17:28:40 - Gera Num Cte.0 - ERROR (version 5.0.1-stable, build 1 from 2013-11-15_16-08-58 by buildguy) : org.pentaho.di.core.exception.KettleValueException:
2016/02/05 17:28:40 - Gera Num Cte.0 - Javascript error:
2016/02/05 17:28:40 - Gera Num Cte.0 - TypeError: Cannot call method "substring" of null (script#12)
2016/02/05 17:28:40 - Gera Num Cte.0 -
2016/02/05 17:28:40 - Gera Num Cte.0 - at org.pentaho.di.trans.steps.scriptvalues_mod.ScriptValuesMod.addValues(ScriptValuesMod.java:457)
2016/02/05 17:28:40 - Gera Num Cte.0 - at org.pentaho.di.trans.steps.scriptvalues_mod.ScriptValuesMod.processRow(ScriptValuesMod.java:692)
2016/02/05 17:28:40 - Gera Num Cte.0 - at org.pentaho.di.trans.step.RunThread.run(RunThread.java:60)
2016/02/05 17:28:40 - Gera Num Cte.0 - at java.lang.Thread.run(Unknown Source)
2016/02/05 17:28:40 - Gera Num Cte.0 - Caused by: org.mozilla.javascript.EcmaError: TypeError: Cannot call method "substring" of null (script#12)
How can I solve this issue, because is in the end of file?

Answer 1

You probably have an extra line in your file, which makes it run with null values.
You should probably filter out the illegal rows before they reach your Java Script step, or check the input values in your function with something like:
function gera_cte (arg1, arg2)
{
if (arg1 == null) {
return arg1;
}
if (arg2 == 0) {
return arg1.substring(3,9);
}
else
{
return arg2.substring(4,10);
}
}
or setting trans_Status = SKIP_TRANSFORMATION; when the arguments are null.

Answer 2

If you are executing this script using the "Modified Javascript Value" step, you have this error because the javascript engine that PDI uses (Mozilla's Rhino engine) doesn't have a "substring" method. Try using "substr" instead:
// Perform the substring function
//
// Usage:
// substr(var, from);
// substr(var, from, to);
//
// 2007-01-25
//
var str1= "Hello Pentaho!";
var str2= substr(str1, 6);
var str3= substr(str1, 6, 7);
Alert("Input : " + str1);
Alert("From position 6: " + str2);
Alert("From position 6 for 7 long : " + str3);