kotlin mutableMapがnullか空であれば空のmapを返す

map名.orEmpty()

fun main() {

    val m = mutableMapOf('a' to 1, 'b' to 2, 'c' to 3, 'd' to 4, 'e' to 5)
    val m2: Map<Char, Int>  = mutableMapOf()
    val m3: Map<Char?, Int?>  = mutableMapOf(null to null)
    val m4: Map<Char, Int>?  = null
        
    println( m.orEmpty() )  // {a=1, b=2, c=3, d=4, e=5}
    println( m2.orEmpty() ) // {}
    println( m3.orEmpty() ) // {null=null}
    println( m4.orEmpty() ) // {}

}