在创建AmazonPollyPresigningClient - signerClass时，AWS Android SDK错误为amazonpollycustompresignerclass为空

When I integrate Polly in my Android application, I am getting 'IllegalArgumentException' because in SignerFactory, Signer is null for signerType - AmazonPollyCustomPresigner. I am using AWS Lex and Polly in the same application. I am using 'com.amazonaws:aws-android-sdk-polly:2.4.2'. In the sample application provided by AWS, with the same credentials, Polly is working fine. In that they have used com.amazonaws:aws-android-sdk-polly:2.3.4. I cannot use it because I already interpreted 2.4.2 with other AWS technologies.When I integrate Polly in my Android applicatio