DynamoDb enhanced client: support UpdateExpressions in single-request update

Author: anasatirbasa

services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/update/UpdateExpressionConverter.java

@@ -73,7 +73,10 @@ private UpdateExpressionConverter() {
      * of whether it represents an update expression, conditional expression or another type of expression, since once
      * the string is generated that update expression is the final format accepted by DDB.
      *
-     * @return an Expression representing the concatenation of all actions in this UpdateExpression
+     * @param expression the UpdateExpression to convert
+     *
+     * @return an Expression representing the concatenation of all actions in this UpdateExpression, or null if the expression
+     * is null or empty
      */
     public static Expression toExpression(UpdateExpression expression) {
         if (expression == null || expression.isEmpty()) {
@@ -91,8 +94,8 @@ public static Expression toExpression(UpdateExpression expression) {
     }
 
     /**
-     * Attempts to find the list of attributes associated with update actions for the supplied {@link UpdateExpression} by
-     * looking at the combined collection of paths and ExpressionName values. Because attribute names can be composed of nested
+     * Attempts to find the list of attribute names that will be updated for the supplied {@link UpdateExpression} by looking at
+     * the combined collection of paths and ExpressionName values. Because attribute names can be composed from nested
      * attribute references and list references, the leftmost part will be returned if composition is detected.
      * <p>
      * Examples: The expression contains a {@link DeleteAction} with a path value of 'MyAttribute[1]'; the list returned

services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/internal/update/UpdateExpressionConverterTest.java

@@ -47,7 +47,15 @@ class UpdateExpressionConverterTest {
     private static final String VALUE_TOKEN = ":PRE_";
 
     @Test
-    void convert_emptyExpression() {
+    void convert_nullUpdateExpression_returnsNullExpression() {
+        UpdateExpression updateExpression = null;
+        Expression expression = UpdateExpressionConverter.toExpression(updateExpression);
+
+        assertThat(expression).isNull();
+    }
+
+    @Test
+    void convert_emptyUpdateExpression_returnsNullExpression() {
         UpdateExpression updateExpression = UpdateExpression.builder().build();
         Expression expression = UpdateExpressionConverter.toExpression(updateExpression);