Hello,
Could you please help in modifying the expression where the null values can be converted to O (zero) in the expression itself (using if … else or anything else) ?

Hi @ajit555,
If Prev_c1 is a mathematical result (due to the c1 values special structure) $["c1"]-1 would do the job. But I don’t think it’s the case. If not (ie previous value is necessary), “value should be 0” is an external information so if($["c1",-1]=MISSING,0,$["c1",-1]) seems to do the job in the first Expression node.
Syntax is different in column expression :

if (isMissing(column("c1",-1)))
{0}
else
{column("c1",-1)}

By the way, I just learn that column("c1",-1) works in column expression !! Which is great : thanks for this !

Yes you could define a intermediate variable. The result “out” is unecessary. See documentation in the description of the node or Column Expressions – KNIME Community Hub
For this node " The syntax and grammar of the expressions are based on the Javascript".