NullPointerException during encoding when creating a transaction with null data

[furkilic]

NullPointerException during encoding when creating a transaction with null data

We are creating a RawTransaction.createTransaction with data = null (data is nullable for a transaction)

Looking at the code data is nullable as null is handled here

web3j/crypto/src/main/java/org/web3j/crypto/transaction/type/LegacyTransaction.java

Line 68 in 1797f5e

this.data = data != null ? Numeric.cleanHexPrefix(data) : null;

However during encoding TransactionEncoder.encode we reach this code where nullsafety is not handled

web3j/crypto/src/main/java/org/web3j/crypto/transaction/type/LegacyTransaction.java

Line 93 in 1797f5e

byte[] data = Numeric.hexStringToByteArray(getData());

Internally Numeric.hexStringToByteArray(getData()) throws a NullPointerException as data is null

Steps To Reproduce

TransactionEncoder.encode(
  RawTransaction.createTransaction(
    BigInteger.ONE,BigInteger.ONE,BigInteger.ONE,"0x0", null
  )
)

Expected behavior

Encoded Transaction returned

Actual behavior

NullPointerException

Environment

• Web3j 4.12.2 (still present in main)

Additional context

[furkilic]

Looking at how data is handled on the utility method when there is no data

web3j/crypto/src/main/java/org/web3j/crypto/transaction/type/LegacyTransaction.java

Line 122 in 1797f5e

return new LegacyTransaction(nonce, gasPrice, gasLimit, to, value, "");

It's safe to assume that data should be empty instead of null in the contructor
this.data = data != null ? Numeric.cleanHexPrefix(data) : "";

I can create the PR if you agree with that.