Fixed NullPointerException in S3 thrown when null metadata value is provided. (#5238)

Author: zoewangg

.changes/next-release/bugfix-AmazonS3-cf52d1d.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "Amazon S3",
+    "contributor": "",
+    "description": "Fixed NullPointerException in S3 thrown when null metadata value is provided."
+}

services/s3/src/main/java/software/amazon/awssdk/services/s3/internal/handlers/ObjectMetadataInterceptor.java

@@ -15,8 +15,8 @@
 
 package software.amazon.awssdk.services.s3.internal.handlers;
 
+import java.util.HashMap;
 import java.util.Map;
-import java.util.stream.Collectors;
 import software.amazon.awssdk.annotations.SdkInternalApi;
 import software.amazon.awssdk.core.SdkRequest;
 import software.amazon.awssdk.core.interceptor.Context;
@@ -69,6 +69,6 @@ private CreateMultipartUploadRequest trimMetadataNames(CreateMultipartUploadRequ
 
     private Map<String, String> trimKeys(Map<String, String> map) {
         return map.entrySet().stream()
-            .collect(Collectors.toMap(e -> StringUtils.trim(e.getKey()), Map.Entry::getValue));
+                  .collect(HashMap::new, (m, e) -> m.put(StringUtils.trim(e.getKey()), e.getValue()), HashMap::putAll);
     }
 }

services/s3/src/test/java/software/amazon/awssdk/services/s3/internal/handlers/ObjectMetadataInterceptorTest.java

@@ -20,6 +20,7 @@
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -71,6 +72,26 @@ public void modifyRequest_putObject_metadataKeysAreTrimmed(TestCase tc) {
         assertThat(modified.metadata().keySet()).containsExactlyElementsOf(tc.expectedKeys);
     }
 
+    @Test
+    public void modifyRequest_putObjectMetadataValueNull_shouldNotThrowException() {
+        Map<String, String> metadata = new HashMap<>();
+        metadata.put("key", null);
+
+        Context.ModifyHttpRequest ctx = mock(Context.ModifyHttpRequest.class);
+
+        PutObjectRequest put = PutObjectRequest.builder()
+                                               .metadata(metadata)
+                                               .build();
+
+        when(ctx.request()).thenReturn(put);
+
+        ExecutionAttributes attrs = new ExecutionAttributes();
+        attrs.putAttribute(SdkExecutionAttribute.OPERATION_NAME, "PutObject");
+
+        PutObjectRequest modified = (PutObjectRequest) INTERCEPTOR.modifyRequest(ctx, attrs);
+        assertThat(modified.metadata().entrySet()).containsExactlyElementsOf(metadata.entrySet());
+    }
+
     @ParameterizedTest
     @MethodSource("testCases")
     public void modifyRequest_creatMultipartUpload_metadataKeysAreTrimmed(TestCase tc) {