Consider optional empty arrays to be absent when finding missing fields

Closes gh-519

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/JsonContentHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2017 the original author or authors.
+ * Copyright 2014-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.restdocs.payload;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
@@ -25,6 +26,8 @@ import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
 
+import org.springframework.restdocs.payload.JsonFieldProcessor.ExtractedField;
+
 /**
  * A {@link ContentHandler} for JSON content.
  *
@@ -70,13 +73,28 @@ class JsonContentHandler implements ContentHandler {
 		for (FieldDescriptor candidate : candidates) {
 			if (candidate.isOptional()
 					&& missing.getPath().startsWith(candidate.getPath())
-					&& !this.fieldProcessor.hasField(candidate.getPath(), payload)) {
+					&& isMissing(candidate, payload)) {
 				return true;
 			}
 		}
 		return false;
 	}
 
+	private boolean isMissing(FieldDescriptor candidate, Object payload) {
+		try {
+			ExtractedField extracted = this.fieldProcessor.extract(candidate.getPath(),
+					payload);
+			if (extracted.getValue() instanceof Collection
+					&& ((Collection<?>) extracted.getValue()).isEmpty()) {
+				return true;
+			}
+			return false;
+		}
+		catch (FieldDoesNotExistException ex) {
+			return true;
+		}
+	}
+
 	@Override
 	public String getUndocumentedContent(List<FieldDescriptor> fieldDescriptors) {
 		Object content = readContent();

spring-restdocs-core/src/test/java/org/springframework/restdocs/payload/JsonContentHandlerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2017 the original author or authors.
+ * Copyright 2014-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -147,4 +147,14 @@ public class JsonContentHandlerTests {
 		assertThat(missingFields.size(), is(equalTo(0)));
 	}
 
+	@Test
+	public void describedFieldThatIsNotPresentNestedBeneathOptionalArrayThatIsEmptyIsNotConsideredMissing() {
+		List<FieldDescriptor> missingFields = new JsonContentHandler(
+				"{\"outer\":[]}".getBytes())
+						.findMissingFields(Arrays.asList(new FieldDescriptor("outer"),
+								new FieldDescriptor("outer[]").optional(),
+								new FieldDescriptor("outer[].inner")));
+		assertThat(missingFields.size(), is(equalTo(0)));
+	}
+
 }