Blank cell in Decision Table results in the omission of the conditional element or constraint for the rule

Issue

• A blank cell in the following Decision Table is causing both Rl1 and Rl3 rules being fired.

    CONDITION     CONDITION
    d=="$param"   c=="$param"

Rules   ID            Name
Rl1 111       Test1
Rl2 222       Test2
Rl3 333 

What is the reason behind this strange behaviour?

• Is there a way to ensure that Rl3 rule will not be fired even if the corresponding cell is blank?