Convert UNIX timestamp to DateTime using Direct Query

Hi, Gurus!
I'm connected to Apache Phoenix through CData Power BI connector using Direct Query.

And i can't solve the problem with convertation UNIX timestamp to DateTime without using importing.

I tried some tasks to resolve this:

• Custom column in Query Editor
  #datetime(1970, 1, 1, 0, 0, 0) + #duration(0, 0, 0, [UnixTime])​
  as a result i had notification about importing my data

• Function + Cutom Column in Query Editor
  Function UnixToDate:
  
  let q = (UnixTime) =>
  let
  Source = (#datetime(1900, 1, 1, 0, 0, 0) + #duration(0, 0, 0, UnixTime))
  in
  Source
  in
  q​
  
  Custom column:
  = UnixToDate([UnixTime])
  result was the same - notification about importing my data

•  New column using DAX in Power BI Desktop
  UTCTime = VAR UnixDays = 'Date'[UnixTime]/(60*60*24)
  RETURN (DATEVALUE("1/1/1970")+UnixDays)
  
  as a result i had an error:
  OLE DB or ODBC error: [Expression.Error] Failed to collapse expression in data source. Try a simpler expression ..
  
  in any use of datevalue and addition results in this error.

Do you know any other methods that you can use with direct query to resolve this?

Converting timestamp to unix timestamp in our datamart was a necessity because we had another mistake with Direct Query and ApachePhoenix. Where timestamp was null in datamart in power bi null becomes default date, and without importing i'm also did not find a solution how to replace default date to null. Because then you use expressions like
if [date] = #datetime(1,1,1900,0,0,0) then null else [date]

you getting an error from database that you can't compare timestamp and varchar

Hope for help in this task. And sorry for my english (: