This is a case where some amount of input resistance is required. It's needed for passive components to operate in their filtering role.
In real life there is some amount of input resistance. It might be present in circuitry upstream. Perhaps it's invisible and unknown. Regardless, it ought to be included in a schematic to show it's understood that input current is not infinite and is purposely limited to a reasonable level.
It's up to the designer to select the proper ohm value so that the filter performs as intended with your chosen L & C values.