Add parameter checks for HadoopTables#create

[chenjunjiedada]

The HadoopTables#create doesn't check whether the spec is null which may lead to NullPointerExeception. For example, a user may use specForTables to get partition spec for a table and then pass it to HadoopTables#create, it throws NullPointerExeception if the table doesn't have partition column.

IIUC we should support creating the table which has no partition. So what is the default behavior? Shall we use a PartitionSpec with an empty PartitionField list?
PartitionSpec.buildfor(shema).build()

[rdblue]

Unpartitioned tables use PartitionSpec.unpartitioned().

[chenjunjiedada]

So it should return PartitionSpec.unpartitioned() for specForTables when it found no partition column.

[rdblue]

Thanks for fixing #292! Do you plan to add more checks for this issue was well?

[chenjunjiedada]

Yes, I will spend some time on this.

[chenjunjiedada]

close via #298