Fix graphql for empty nested fields.

backend/src/Squidex.Domain.Apps.Entities/Contents/GraphQL/Types/Contents/FieldInputVisitor.cs

@@ -21,6 +21,11 @@ namespace Squidex.Domain.Apps.Entities.Contents.GraphQL.Types.Contents
 
         public IGraphType? Visit(IArrayField field, FieldInfo args)
         {
+            if (args.Fields.Count == 0)
+            {
+                return null;
+            }
+
             var schemaFieldType =
                 new ListGraphType(
                     new NonNullGraphType(

backend/src/Squidex.Domain.Apps.Entities/Contents/GraphQL/Types/Contents/FieldVisitor.cs

@@ -97,6 +97,11 @@ namespace Squidex.Domain.Apps.Entities.Contents.GraphQL.Types.Contents
 
         public (IGraphType?, IFieldResolver?, QueryArguments?) Visit(IArrayField field, FieldInfo args)
         {
+            if (args.Fields.Count == 0)
+            {
+                return default;
+            }
+
             var schemaFieldType =
                 new ListGraphType(
                     new NonNullGraphType(
@@ -152,7 +157,7 @@ namespace Squidex.Domain.Apps.Entities.Contents.GraphQL.Types.Contents
 
         public (IGraphType?, IFieldResolver?, QueryArguments?) Visit(IField<UIFieldProperties> field, FieldInfo args)
         {
-            return (null, null, null);
+            return default;
         }
 
         private (IGraphType?, IFieldResolver?, QueryArguments?) ResolveReferences(IField<ReferencesFieldProperties> field, FieldInfo args)
@@ -165,7 +170,7 @@ namespace Squidex.Domain.Apps.Entities.Contents.GraphQL.Types.Contents
 
                 if (!union.PossibleTypes.Any())
                 {
-                    return (null, null, null);
+                    return default;
                 }
 
                 contentType = union;

backend/tests/Squidex.Domain.Apps.Entities.Tests/Contents/GraphQL/GraphQLTestBase.cs

@@ -100,6 +100,8 @@ namespace Squidex.Domain.Apps.Entities.Contents.GraphQL
                         new GeolocationFieldProperties())
                     .AddTags(14, "my-tags", Partitioning.Invariant,
                         new TagsFieldProperties())
+                    .AddArray(20, "my-empty-array", Partitioning.Invariant, null,
+                        new ArrayFieldProperties())
                     .AddArray(15, "my-array", Partitioning.Invariant, f => f
                         .AddBoolean(121, "nested-boolean")
                         .AddNumber(122, "nested-number")