Fails to parse an asset ID string with no tokenId

[ra-phael]

From my understanding of CAIP-19, the tokenId suffix is optional, as in the example provided for DAI under Test Cases:

# DAI Token
eip155:1/erc20:0x6b175474e89094c44da98b954eedeac495271d0f

However this test doesn't pass using that exact same string:

 it("should instantiate from string", async () => {
    const result = new AssetId(
      "eip155:1/erc20:0x6b175474e89094c44da98b954eedeac495271d0f"
    );
    assertInterface(result);
  });