Add a test that shows problem with sometimes null field within an array

Closes gh-399

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

@@ -378,6 +378,23 @@ public class ResponseFieldsSnippetTests extends AbstractSnippetTests {
 										.build());
 	}
 
+	@Test
+	public void responseWithSomeNullOcurrencesOfAField() throws IOException {
+		this.snippets.expectResponseFields()
+				.withContents(tableWithHeader("Path", "Type", "Description")
+						.row("`assets[].name`", "`String`", "one"));
+		new ResponseFieldsSnippet(Arrays.asList(
+				fieldWithPath("assets[].name").description("one")))
+				.document(this.operationBuilder.response()
+						.content(
+								"{\"assets\": [" +
+										"{\"name\": \"sample1\"}, " +
+										"{\"name\": null}, " +
+										"{\"name\": \"sample2\"}]}")
+						.build());
+	}
+
+
 	private String escapeIfNecessary(String input) {
 		if (this.templateFormat.equals(TemplateFormats.markdown())) {
 			return input;