It's quite common to want to use the class to merely get price info and similar, for which an address and private key isn't needed.

We should probably add the ability for users to instantiate the class without them. My current workaround is to simply use 0x0000000000000000000000000000000000000000 as the address and 0x0000000000000000000000000000000000000000000000000000000000000000 as the priv key.