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Filtering Out Newly Listed Companies

I am looking to filter out companies in the Pipeline that have less than 1yr of trading history. Simply trying to drop records with NANs returns an error for me, wondering what the best way to drop these names would be?
My attempt:

 price_hist = np.isnan(USEquityPricing.close[-270]) == False  

TypeError: zipline.pipeline.term.getitem() expected a value of
type zipline.assets._assets.Asset for argument 'key', but got int