Wrong matched rules set were fired when one of the condition having empty cell in drools 6.5.0 using Jdk 1.8

In JDK 1.7 we were using Drools 5.3.0.Final version and we are migrating to jdk 1.8 so drools 5.3.0.Final was not supported in which we were using Package Builder.
We migrated JDK 1.8 with drools 6.5.0.Final which uses Kie API to implement rules

Below is the decision table I am using:

Customer Rule:

Condition Condition Action
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Rule NO. Type Years Discount
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1 "Individual" 5 15
2 "Individual" 3 10
3 "Individual" 20

if I insert customer object as "Type" = Individual and "Years" = 5
after fireAllRules
It fires two rules i.e Rule no. 1 and 3 and gives the 3rd Rule number as result instead of Rule number 1, inturn gives Discount as 20 instead of 15 which is wrong result.
if I insert customer object as "Type" = Individual and "Years" = 3
after fireAllRules
It fires two rules i.e Rule no. 2 and 3 and gives the 3rd rule number as result instead of Rule number 2, inturn gives Discount as 20 instead of 10 which is wrong result.

Exact rule match is not happening and providing wrong results.

Could you please give the solution for this it is breaking so many rules in the application.