Add null test

Author: haydenbaker

core/http-auth-aws/src/test/java/software/amazon/awssdk/http/auth/aws/internal/signer/DefaultAwsV4HttpSignerTest.java

@@ -308,4 +308,19 @@ public void sign_WithPayloadSigningFalseAndHttp_FallsBackToPayloadSigning() {
         assertThat(signedRequest.request().firstMatchingHeader("x-amz-content-sha256"))
             .hasValue("a15c8292b1d12abbbbe4148605f7872fbdf645618fee5ab0e8072a7b34f155e2");
     }
+
+    @Test
+    public void sign_WithPayloadSigningNullAndHttp_FallsBackToPayloadSigning() {
+        SignRequest<? extends AwsCredentialsIdentity> request = generateBasicRequest(
+            AwsCredentialsIdentity.create("access", "secret"),
+            httpRequest -> httpRequest.uri(URI.create("http://demo.us-east-1.amazonaws.com")),
+            signRequest -> signRequest
+                .putProperty(PAYLOAD_SIGNING_ENABLED, null)
+        );
+
+        SignedRequest signedRequest = signer.sign(request);
+
+        assertThat(signedRequest.request().firstMatchingHeader("x-amz-content-sha256"))
+            .hasValue("a15c8292b1d12abbbbe4148605f7872fbdf645618fee5ab0e8072a7b34f155e2");
+    }
 }