diff --git a/src/main/kotlin/com/uchuhimo/konf/Config.kt b/src/main/kotlin/com/uchuhimo/konf/Config.kt
index cb521e45..781ec659 100644
--- a/src/main/kotlin/com/uchuhimo/konf/Config.kt
+++ b/src/main/kotlin/com/uchuhimo/konf/Config.kt
@@ -311,7 +311,15 @@ private class ConfigImpl constructor(
                     }
                 is ValueState.Value -> valueState.value as T
                 is ValueState.Lazy<*> -> {
-                    val value = valueState.thunk(lazyContext)!!
+                    val value = try {
+                        valueState.thunk(lazyContext)
+                    } catch (exception: UnsetValueException) {
+                        if (errorWhenUnset) {
+                            throw exception
+                        } else {
+                            return null
+                        }
+                    }
                     if (item.type.rawClass.isInstance(value)) {
                         value as T
                     } else {
@@ -558,7 +566,7 @@ private class ConfigImpl constructor(
 
     private sealed class ValueState {
         object Unset : ValueState()
-        data class Lazy<T>(var thunk: (config: ItemContainer) -> T) : ValueState()
+        data class Lazy<T : Any>(var thunk: (config: ItemContainer) -> T) : ValueState()
         data class Value(var value: Any) : ValueState()
     }
 }
diff --git a/src/test/kotlin/com/uchuhimo/konf/ConfigSpek.kt b/src/test/kotlin/com/uchuhimo/konf/ConfigSpek.kt
index 2103698b..41632161 100644
--- a/src/test/kotlin/com/uchuhimo/konf/ConfigSpek.kt
+++ b/src/test/kotlin/com/uchuhimo/konf/ConfigSpek.kt
@@ -134,6 +134,29 @@ object ConfigSpek : SubjectSpek<Config>({
                 assertThat(newConfig[spec.type], equalTo(NetworkBuffer.Type.ON_HEAP))
                 assertThat(newConfig, equalTo(subject))
             }
+            it("should not contain unset items in map") {
+                val config = Config { addSpec(spec) }
+                assertThat(config.toMap(), equalTo(mapOf(
+                        spec.name.name to "buffer",
+                        spec.type.name to NetworkBuffer.Type.OFF_HEAP)))
+            }
+        }
+        on("object methods") {
+            val map = mapOf(
+                    spec.name.name to "buffer",
+                    spec.type.name to NetworkBuffer.Type.OFF_HEAP)
+            it("should not equal to object of other class") {
+                assertFalse(subject.equals(1))
+            }
+            it("should equal to itself") {
+                assertThat(subject, equalTo(subject))
+            }
+            it("should have same hash code with map with same content") {
+                assertThat(subject.hashCode(), equalTo(map.hashCode()))
+            }
+            it("should convert to string in map-like format") {
+                assertThat(subject.toString(), equalTo("Config(items=$map)"))
+            }
         }
         group("get operation") {
             on("get with valid item") {