DB2 - error getting substring if "from position" is out of range

If second argument of a SUBSTRING(x,y,z) function is out of range of first argument an exception is thrown [1]. Source-specific command [2].

[1]
Caused by: com.ibm.db2.jcc.am.SqlDataException: DB2 SQL Error: SQLCODE=-138, SQLSTATE=22011, SQLERRMC=null, DRIVER=4.12.55
at com.ibm.db2.jcc.am.hd.a(hd.java:668)
at com.ibm.db2.jcc.am.hd.a(hd.java:60)
...

[2]
SELECT substr(varchar(g_0.TimestampValue), 40, CASE WHEN 0 > (length(varchar(g_0.TimestampValue)) - (40 - 1)) THEN (length(varchar(g_0.TimestampValue)) - (40 - 1)) ELSE 0 END) FROM SmallA AS g_0 WHERE g_0.IntKey = 1