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<String, String> = 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<String, String>
Found:
Map<String, String>?

so how to handle above error? should I change the method declaration in interface? or any other technique to fix this properly? I am not sure how the coding style in Kotlin. I am new to Kotlin.

You can use let or just give default value for extraDtls if it is null.

// solution 1
var extraDtls = calculate(val1, val2)
extraDtls?.let { makeItHappenImpl.methodOne(it) }

// solution 2
// using elvis operator (?:) if it is null take the right value otherwise take left value
var extraDtls = calculate(val1, val2) ?: emptyMap()
makeItHappenImpl.methodOne(extraDtls)