docs(lib-dynamodb): add details to description of removeUndefinedValues (#6710)

Author: kuhe

lib/lib-dynamodb/README.md

@@ -105,7 +105,11 @@ export interface marshallOptions {
    */
   convertEmptyValues?: boolean;
   /**
-   * Whether to remove undefined values while marshalling.
+   * Whether to remove undefined values from JS arrays/Sets/objects
+   * when marshalling to DynamoDB lists/sets/maps respectively.
+   *
+   * A DynamoDB item is not itself considered a map. Only
+   * attributes of an item are examined.
    */
   removeUndefinedValues?: boolean;
   /**

packages/util-dynamodb/src/marshall.ts

@@ -13,7 +13,11 @@ export interface marshallOptions {
    */
   convertEmptyValues?: boolean;
   /**
-   * Whether to remove undefined values while marshalling.
+   * Whether to remove undefined values from JS arrays/Sets/objects
+   * when marshalling to DynamoDB lists/sets/maps respectively.
+   *
+   * A DynamoDB item is not itself considered a map. Only
+   * attributes of an item are examined.
    */
   removeUndefinedValues?: boolean;
   /**