Added NPE guard

spring-cloud-contract-wiremock/src/main/java/org/springframework/cloud/contract/wiremock/restdocs/ContractExchangeHandler.java

@@ -21,6 +21,7 @@ import java.lang.reflect.Field;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -91,6 +92,9 @@ public class ContractExchangeHandler
 		@SuppressWarnings("unchecked")
 		Map<String, Object> map = (((Map<String, Map<String, Object>>) ReflectionUtils
 				.getField(field, null)).get(index));
+		if (map == null) {
+			return new HashMap<>();
+		}
 		return map;
 	}