public Map<String, String> getCustomRequestHeaders() {
        if (customRequestHeaders == null) {
            return null;
        }
        return Collections.unmodifiableMap(customRequestHeaders);
    }
Returns an immutable map of custom header names to header values.

@return The immutable map of custom header names to header values.
aws-java-sdk-core/src/main/java/com/amazonaws/AmazonWebServiceRequest.java