Collection adapter nullsafety

It seems passing a null map/list for serialization throws an NPE

Author: SentryMan

json-core/src/main/java/io/avaje/json/core/CollectionAdapter.java

@@ -83,6 +83,10 @@ public C fromJson(JsonReader reader) {
 
   @Override
   public void toJson(JsonWriter writer, C value) {
+    if (value == null) {
+      writer.nullValue();
+      return;
+    }
     if (value.isEmpty()) {
       writer.emptyArray();
       return;

json-core/src/main/java/io/avaje/json/core/MapAdapter.java

@@ -30,7 +30,7 @@
 final class MapAdapter<V> implements JsonAdapter<Map<String, V>> {
 
   static <V> JsonAdapter<Map<String, V>> create(JsonAdapter<V> valueAdapter) {
-    return new MapAdapter<>(valueAdapter);
+    return new MapAdapter<>(valueAdapter).nullSafe();
   }
 
   private final JsonAdapter<V> valueAdapter;

json-core/src/test/java/io/avaje/json/core/CoreTypesTest.java

@@ -1,16 +1,17 @@
 package io.avaje.json.core;
 
-import io.avaje.json.JsonAdapter;
-import io.avaje.json.JsonReader;
-import io.avaje.json.stream.BufferedJsonWriter;
-import io.avaje.json.stream.JsonStream;
-import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.assertThat;
 
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
-import static org.assertj.core.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+import io.avaje.json.JsonAdapter;
+import io.avaje.json.JsonReader;
+import io.avaje.json.stream.BufferedJsonWriter;
+import io.avaje.json.stream.JsonStream;
 
 class CoreTypesTest {
 
@@ -36,6 +37,17 @@ void mapOfScalar() {
     assertThat(fromJsonMap).containsOnlyKeys("one", "two");
   }
 
+  @Test
+  void nullMap() {
+    JsonAdapter<Long> longAdapter = CoreTypes.create(Long.class);
+    JsonAdapter<Map<String, Long>> mapAdapter = CoreTypes.createMap(longAdapter);
+
+    BufferedJsonWriter writer = stream.bufferedWriter();
+    mapAdapter.toJson(writer, null);
+    String asJson = writer.result();
+    assertThat(asJson).isEmpty();
+  }
+
   @Test
   void listOfScalar() {
     JsonAdapter<Long> longAdapter = CoreTypes.create(Long.class);
@@ -54,6 +66,17 @@ void listOfScalar() {
     assertThat(fromJsnoList).containsExactly(54L, 21L, 63L);
   }
 
+  @Test
+  void nullList() {
+    JsonAdapter<Long> longAdapter = CoreTypes.create(Long.class);
+    JsonAdapter<List<Long>> listAdapter = CoreTypes.createList(longAdapter);
+
+    BufferedJsonWriter writer = stream.bufferedWriter();
+    listAdapter.toJson(writer, null);
+    String asJson = writer.result();
+    assertThat(asJson).isEmpty();
+  }
+
   @SuppressWarnings("unchecked")
   @Test
   void createCoreAdapters() {