Making sure we infer the content-type on streaming operations and actually add it (unless there's already a non-blank Content-Type)

Author: kiiadi

core/src/main/java/software/amazon/awssdk/core/runtime/transform/StreamingRequestMarshaller.java

@@ -17,6 +17,7 @@
 
 import static software.amazon.awssdk.http.Headers.CONTENT_LENGTH;
 import static software.amazon.awssdk.http.Headers.CONTENT_TYPE;
+import static software.amazon.awssdk.utils.StringUtils.isBlank;
 import static software.amazon.awssdk.utils.Validate.paramNotNull;
 
 import software.amazon.awssdk.annotations.SdkProtectedApi;
@@ -47,7 +48,7 @@ public StreamingRequestMarshaller(Marshaller<Request<T>, T> delegate, RequestBod
     public Request<T> marshall(T in) {
         Request<T> marshalled = delegate.marshall(in);
         marshalled.setContent(requestBody.asStream());
-        if (!marshalled.getHeaders().containsKey(CONTENT_TYPE)) {
+        if (!marshalled.getHeaders().containsKey(CONTENT_TYPE) || isBlank(marshalled.getHeaders().get(CONTENT_TYPE))) {
             marshalled.addHeader(CONTENT_TYPE, requestBody.contentType());
         }