diff --git a/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/Json.java b/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/Json.java
index a046f0a..34e1ebd 100644
--- a/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/Json.java
+++ b/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/Json.java
@@ -13,6 +13,7 @@ import java.io.Reader;
 import java.io.StringWriter;
 import java.time.Instant;
 import java.util.Map;
+import java.util.Objects;
 import java.util.function.Consumer;
 
 public class Json implements DataStructure {
@@ -37,11 +38,14 @@ public class Json implements DataStructure {
     }
 
     public static String toString(Map<String, Object> map) throws IOException {
-        return INSTANCE.createBuilder().buildMap(map).build();
+        return map != null ? INSTANCE.createBuilder().buildMap(map).build() : null;
     }
 
     @SuppressWarnings("unchecked")
     public static Map<String, Object> toMap(String json) {
+        if (json == null) {
+            return null;
+        }
         PlainParser parser = new PlainParser();
         parser.parse(json);
         Object object = parser.getResult();
@@ -52,6 +56,7 @@ public class Json implements DataStructure {
     }
 
     public static Map<String, Object> toMap(Reader reader) throws IOException {
+        Objects.requireNonNull(reader);
         // buffered reader is required for mark() support
         try (BufferedReader bufferedReader = new BufferedReader(reader)){
             return JsonGenerator.toMap(INSTANCE.createParser().parse(bufferedReader));
diff --git a/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/JsonBuilder.java b/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/JsonBuilder.java
index 458c6b0..ba4af5b 100644
--- a/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/JsonBuilder.java
+++ b/datastructures-json-tiny/src/main/java/org/xbib/datastructures/json/tiny/JsonBuilder.java
@@ -112,6 +112,13 @@ public class JsonBuilder implements Builder {
     @SuppressWarnings("unchecked")
     @Override
     public Builder buildValue(Object object) throws IOException {
+        if (object instanceof Map) {
+            buildMap((Map<String, Object>) object);
+            return this;
+        } else if (object instanceof Collection) {
+            buildCollection((Collection<Object>) object);
+            return this;
+        }
         if (state.structure == Structure.MAP || state.structure == Structure.KEY) {
             beginValue(object);
         } else if (state.structure == Structure.COLLECTION) {
@@ -119,11 +126,6 @@ public class JsonBuilder implements Builder {
         }
         if (object == null) {
             buildNull();
-            return this;
-        } else if (object instanceof Map) {
-            buildMap((Map<String, Object>) object);
-        } else if (object instanceof Collection) {
-            buildCollection((Collection<Object>) object);
         } else if (object instanceof CharSequence) {
             buildString((CharSequence) object, true);
         } else if (object instanceof Boolean) {
@@ -161,8 +163,7 @@ public class JsonBuilder implements Builder {
     public Builder buildKey(CharSequence string) throws IOException {
         if (state.structure == Structure.COLLECTION) {
             beginArrayValue(string);
-        }
-        if (state.structure == Structure.MAP || state.structure == Structure.KEY) {
+        } else if (state.structure == Structure.MAP || state.structure == Structure.KEY) {
             beginKey(string != null ? string.toString() : null);
         }
         buildString(string, true);
diff --git a/datastructures-json-tiny/src/test/java/org/xbib/datastructures/json/tiny/test/JsonBuilderTest.java b/datastructures-json-tiny/src/test/java/org/xbib/datastructures/json/tiny/test/JsonBuilderTest.java
index d6d61a8..326510b 100644
--- a/datastructures-json-tiny/src/test/java/org/xbib/datastructures/json/tiny/test/JsonBuilderTest.java
+++ b/datastructures-json-tiny/src/test/java/org/xbib/datastructures/json/tiny/test/JsonBuilderTest.java
@@ -194,6 +194,15 @@ public class JsonBuilderTest {
         assertEquals("{\"collection\":[{\"a\":\"b\"},{\"c\":\"d\"}]}", jsonBuilder.build());
     }
 
+    @Test
+    public void testListOfMapAsField() throws Exception {
+        JsonBuilder jsonBuilder = new JsonBuilder();
+        jsonBuilder.beginMap();
+        jsonBuilder.field("collection", List.of(Map.of("a","b"), Map.of("c", "d")));
+        jsonBuilder.endMap();
+        assertEquals("{\"collection\":[{\"a\":\"b\"},{\"c\":\"d\"}]}", jsonBuilder.build());
+    }
+
     @Test
     public void testCollectionOfEmptyMaps() throws Exception {
         JsonBuilder jsonBuilder = new JsonBuilder();