[rules-users] NullPointerException with Wrapper objects

[dhai]

I am facing problems which many have encountered in the past. I searched
forums but could not get precise answer. The problem is with null values in
Wrapper objects. See the following code:

rule "Null Check " salience 100
        when
                Salary ( ld : loanDeduction==null || < 0f ) // loanDeduction
is java.lang.Float
        then
                log("Load return is null"); //Global function
                ld = 0f;
end

rule "Nett Salary" salience 70
        when
                Salary ( nett != ( gross – loanDeduction – pf) )
        then
                log("Invalid nett salary amount");
end

You may have idea what I am trying to do. But I get NullPointerException in
“Nett Salary” rule when I fire the rules having fact with null in the
loanDeduction attribute. I believe my “Null Check” exception should execute
first and it does when I put negative value in loadDeduction. What is
solution in such a case? 
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