Unable to change the Datatype to Date/Time in Azure Power Query

Hi @microsoft community

In Azure ADF Power Query i am changing the Data type to Date. But Its getting error. 

Before Chaging Datatype image

After Changing the Date/time datatype getting the error in below image

Error got like this expression.error: Unsupported Constant null

Can anyone pls helpme for solving the error.

Thanks in advance.