trivial change to remove a compilation warning; patched by Jun Rao

clients/src/main/java/org/apache/kafka/common/protocol/types/Struct.java

@@ -86,7 +86,7 @@ public class Struct {
     /**
      * Check if the struct contains a field.
      * @param name
-     * @return
+     * @return Whether a field exists.
      */
     public boolean hasField(String name) {
         return schema.get(name) != null;