Added proposed decorator for fixing rendering issue (fix #66)

Author: oliemansm

src/main/java/graphql/servlet/DefaultGraphQLErrorHandler.java

@@ -2,6 +2,7 @@
 
 import graphql.ExceptionWhileDataFetching;
 import graphql.GraphQLError;
+import graphql.execution.NonNullableFieldWasNullError;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -24,25 +25,26 @@ public List<GraphQLError> processErrors(List<GraphQLError> errors) {
             clientErrors.add(new GenericGraphQLError("Internal Server Error(s) while executing query"));
 
             errors.stream()
-                .filter(error -> !isClientError(error))
-                .forEach(error -> {
-                    if(error instanceof Throwable) {
-                        log.error("Error executing query!", (Throwable) error);
-                    } else if (error instanceof ExceptionWhileDataFetching) {
-                        log.error("Error executing query {}", error.getMessage(), ((ExceptionWhileDataFetching) error).getException());
-                    } else {
-                        log.error("Error executing query ({}): {}", error.getClass().getSimpleName(), error.getMessage());
-                    }
-                });
+                    .filter(error -> !isClientError(error))
+                    .forEach(error -> {
+                        if (error instanceof Throwable) {
+                            log.error("Error executing query!", (Throwable) error);
+                        } else if (error instanceof ExceptionWhileDataFetching) {
+                            log.error("Error executing query {}", error.getMessage(), ((ExceptionWhileDataFetching) error).getException());
+                        } else {
+                            log.error("Error executing query ({}): {}", error.getClass().getSimpleName(), error.getMessage());
+                        }
+                    });
         }
 
         return clientErrors;
     }
 
     protected List<GraphQLError> filterGraphQLErrors(List<GraphQLError> errors) {
         return errors.stream()
-            .filter(this::isClientError)
-            .collect(Collectors.toList());
+                .filter(this::isClientError)
+                .map(this::replaceNonNullableFieldWasNullError)
+                .collect(Collectors.toList());
     }
 
     protected boolean isClientError(GraphQLError error) {
@@ -51,4 +53,12 @@ protected boolean isClientError(GraphQLError error) {
         }
         return !(error instanceof Throwable);
     }
+
+    private GraphQLError replaceNonNullableFieldWasNullError(GraphQLError error) {
+        if (error instanceof NonNullableFieldWasNullError) {
+            return new RenderableNonNullableFieldWasNullError((NonNullableFieldWasNullError) error);
+        } else {
+            return error;
+        }
+    }
 }

src/main/java/graphql/servlet/RenderableNonNullableFieldWasNullError.java

@@ -0,0 +1,52 @@
+package graphql.servlet;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import graphql.ErrorType;
+import graphql.GraphQLError;
+import graphql.execution.NonNullableFieldWasNullError;
+import graphql.language.SourceLocation;
+
+import java.util.List;
+import java.util.Map;
+
+class RenderableNonNullableFieldWasNullError implements GraphQLError {
+
+    private final NonNullableFieldWasNullError delegate;
+
+    public RenderableNonNullableFieldWasNullError(NonNullableFieldWasNullError nonNullableFieldWasNullError) {
+        this.delegate = nonNullableFieldWasNullError;
+    }
+
+    @Override
+    public String getMessage() {
+        return delegate.getMessage();
+    }
+
+    @Override
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    public List<SourceLocation> getLocations() {
+        return delegate.getLocations();
+    }
+
+    @Override
+    public ErrorType getErrorType() {
+        return delegate.getErrorType();
+    }
+
+    @Override
+    public List<Object> getPath() {
+        return delegate.getPath();
+    }
+
+    @Override
+    public Map<String, Object> toSpecification() {
+        return delegate.toSpecification();
+    }
+
+    @Override
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    public Map<String, Object> getExtensions() {
+        return delegate.getExtensions();
+    }
+
+}