diff --git a/spring-web/src/main/java/org/springframework/http/converter/FormHttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/FormHttpMessageConverter.java
index ab2d70d34bf3..088fe8362475 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/FormHttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/FormHttpMessageConverter.java
@@ -334,6 +334,7 @@ protected String serializeForm(MultiValueMap<String, Object> formData, Charset c
 						if (builder.length() != 0) {
 							builder.append('&');
 						}
+						Assert.notNull(name, "Name must not be null");
 						builder.append(URLEncoder.encode(name, charset.name()));
 						if (value != null) {
 							builder.append('=');