diff --git a/modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/OpenAPIDeserializer.java b/modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/OpenAPIDeserializer.java
index 39b67d142e..542b30878b 100644
--- a/modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/OpenAPIDeserializer.java
+++ b/modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/util/OpenAPIDeserializer.java
@@ -846,7 +846,7 @@ public String getString(String key, ObjectNode node, boolean required, String lo
 			}
 		} else if (!v.isValueNode()) {
 			result.invalidType(location, key, "string", node);
-		} else {
+		} else if (!v.isNull()) {
 			value = v.asText();
 			if (uniqueValues != null && !uniqueValues.add(value)) {
 				result.unique(location, "operationId");