Don't throw NoSuchElement if key is missing in the map in `Mapper.rea…

…dNotNullMark`,

because tag can be only prefix for nested object

Fixes #182

runtime/common/src/main/kotlin/kotlinx/serialization/Tagged.kt

@@ -360,7 +360,12 @@ object Mapper {
     class InNullableMapper(val map: Map<String, Any?>) : NamedValueInput() {
         override fun readTaggedValue(tag: String): Any = map.getValue(tag)!!
 
-        override fun readTaggedNotNullMark(tag: String): Boolean = map.getValue(tag) != null
+        override fun readTaggedNotNullMark(tag: String): Boolean {
+            return tag !in map || // in case of complex object, its fields are
+                    // prefixed with dot and there are no 'clean' tag with object name.
+                    // Invalid tags can be handled later, in .readValue
+            map.getValue(tag) != null
+        }
     }
 
     inline fun <reified T : Any> map(obj: T): Map<String, Any> {
@@ -384,4 +389,4 @@ object Mapper {
         val m = InNullableMapper(map)
         return m.read()
     }
-}
+}

runtime/common/src/test/kotlin/kotlinx/serialization/MapperTest.kt

@@ -1,7 +1,6 @@
 package kotlinx.serialization
 
-import kotlin.test.Test
-import kotlin.test.assertEquals
+import kotlin.test.*
 
 class MapperTest {
 
@@ -14,6 +13,13 @@ class MapperTest {
     @Serializable
     data class NullableData(val nullable: String?, val nullable2: String?, val property: String)
 
+    @Serializable
+    data class Category(var name: String? = null,
+                        var subCategory: SubCategory? = null)
+
+    @Serializable
+    data class SubCategory(var name: String? = null)
+
     @Test
     fun testListTagStack() {
         val data = Data(listOf("element1"), "property")
@@ -48,4 +54,26 @@ class MapperTest {
         assertEquals(data.nullable2, unmap.nullable2)
         assertEquals(data.property, unmap.property)
     }
+
+    @Test
+    fun testNestedNull() {
+        val category = Category(name = "Name")
+        val map = Mapper.mapNullable(category)
+        val recreatedCategory = Mapper.unmapNullable<Category>(map)
+        assertEquals(category, recreatedCategory)
+    }
+
+    @Test
+    fun testNestedNullable() {
+        val category = Category(name = "Name", subCategory = SubCategory())
+        val map = Mapper.mapNullable(category)
+        val recreatedCategory = Mapper.unmapNullable<Category>(map)
+        assertEquals(category, recreatedCategory)
+    }
+
+    @Test
+    fun failsOnIncorrectMaps() {
+        val map: Map<String, Any?> = mapOf("name" to "Name")
+        assertFailsWith<NoSuchElementException> { Mapper.unmapNullable<Category>(map) }
+    }
 }