Get ETF Holdings using RDP Python Library

Hi, I am trying to get the holdings for an ETF using the RDP Python Library but I keep getting a `None` response. Here is my code:

import refinitiv.dataplatform as rdp
import pandas as pd


rdp.open_platform_session(
    'APP_KEY', 
    rdp.GrantPassword(
        'MY_USERNAME', 
        'MY_PASSWORD'
    )
)

x = rdp.get_data(universe='IWM',fields= ['TR.FundHoldingRIC','TR.FundHoldingName',
'TR.FundPercentageOfFundAssets',
'TR.FundNumberOfShares',
'TR.FundNumberOfSharesChanged'])#, {'SDate': '2021-01-01'})
print(x)

In this case, `x=None`. Could not find any documentation for how to retrieve this data using the RDP library. I know it can be pulled using Eikon, but I don't want to have to have it open in the background. I would like direct api access to the holdings using nothing but the key