java.util.NoSuchElementException: List is empty when decodeFromJsonElement with nullable type

[tom5079]

Describe the bug
java.util.NoSuchElementException is raised when decodeFromJsonElement with nullable type is called

To Reproduce

@Serializable
data class A(val a: Int)

@Test
fun test() {
    val a = A(42)
    
    val json = Json.encodeToString(a)
    val jsonElement = Json.parseToJsonElement(json)
    
    print(Json.decodeFromString<A?>(json))               // A(a=42)
    print(Json.decodeFromJsonElement<A?>(jsonElement))   // java.util.NoSuchElementException
}

Expected behavior
Successful decode

Environment

• Kotlin version: 1.4.0
• Library version: 1.0.0-RC
• Kotlin platforms: JVM
• Gradle version: 6.3