Pass null value when method declaration creates an empty map - input: Map<String, String> = emptyMap() in the interface - Kotlin I have an interface with following declaration. interface makeItHappenInterface { fun methodOne(params: Map = emptyMap()):Boolean } I want to call this method but the params sometimes could be null. .... var extraDtls = calculate(val1, val2) makeItHappenImpl.methodOne(extraDtls) // error in above line saying ---- Type mismatch. Required: Map Found: Map? so how to handle above error? should I change the method declaration in interface? or any other technique to fix this...