web3j/web3j

Hi all,

I am stucked with one issue while transferring ERC1155 using the contract's wrapper class. I keep getting null pointer exception at send. Below is the code. Check comment where I get null pointer.

public String safeTransferFrom() throws Exception {

    String fromAddress="fromAddress";
    String toAddress="toAddress";
    BigInteger value=BigInteger.valueOf(1);
    Web3j web3j=Web3j.build(new HttpService("https://mainnet.infura.io/v3/<API KEY>"));
    String contractAddress = "0xfaaFDc07907ff5120a76b34b731b278c38d6043C";
    String tokenId="0x3800000000000d1b000000000000000000000000000000000000000000000000";
    byte[] data=new byte[0];

    BigInteger token1;
    token1=new BigInteger(tokenId.substring(2),16);

    Credentials credentials = Credentials.create("privateKey");

    ERC1155 token = ERC1155.load(contractAddress, web3j, credentials, null);

    //getting Null pointer at SEND.
    TransactionReceipt setApproval=token.setApprovalForAll(fromAddress, true).send();
    String approvalHash=setApproval.getTransactionHash();
    log.info("Approval Status Hash >>>>> " +approvalHash);

    //getting Null pointer at SEND.
    TransactionReceipt sendToken=token.safeTransferFrom(fromAddress, toAddress, token1,value,data).send();
    String txHash=sendToken.getTransactionHash();

    if (txHash==null){
        String error="Not sent";
        log.info(error);
        return error;
    }
    else {
        log.info("tx Hash >>>>>>> " + txHash);
        TransactionReceiptProcessor receiptProcessor = new PollingTransactionReceiptProcessor(
                web3j,
                TransactionManager.DEFAULT_POLLING_FREQUENCY,
                TransactionManager.DEFAULT_POLLING_ATTEMPTS_PER_TX_HASH);
        TransactionReceipt txReceipt = receiptProcessor.waitForTransactionReceipt(txHash);
        log.info("Transaction Receipt >>>>> " +txReceipt);
        return txHash;
    }
}