HANA SUBSTRING function inconsistent with teiid behaviour

When querying HANA using hana translator, there is an inconsistency in handling SUBSTRING with similar parameters:

SELECT SUBSTRING('sth',20,1) FROM tablename

That is, when the starting offset supplied to SUBSTRING function is greater than the length of the string value, Teiid returns NULL in this case.
But when I run:

SELECT SUBSTRING(STRINGNUM,20,1) FROM bqt1.smalla

(it is pushed to HANA and STRINGNUM column contains strings of length <=2)
I get empty strings instead of NULL values, which is default in Teiid.

This inconsistency is caused by different handling of such situation on HANA's side.