Blank past ability entries

The past_abilites field in pokemon endpoint has some redundant data which points to no actual ability for example for bulbasaur (1)

"past_abilities": [
    {
        "abilities": [
            {
                "ability": null,
                "is_hidden": true,
                "slot": 3
            }
        ],
        "generation": {
            "name": "generation-iv",
            "url": "https://pokeapi.co/api/v2/generation/4/"
        }
    }
]

imo either it should point to an ability resource or the past_abilities array should be empty also idt bulbasaur got any change of abilities and this issue is across a bunch of pokemon where the ability_id is blank in here https://github.com/PokeAPI/pokeapi/blob/master/data/v2/csv/pokemon_abilities_past.csv which is causing this

think historically it got added somewhere around here in this commit https://github.com/PokeAPI/pokeapi/commit/b23cd6fb3049eb493f64b4cd9de05cbeea8d93d9 removing the rows with blank entries should fix it

just wanted to ask tho was there any reason why it was added that I might be missing? thank you :)

cc: @jemarq04

Start with data/v2/csv/pokemon_abilities_past.csv and compare the affected rows with the response from the Pokémon endpoint. Review commit b23cd6fb3049eb493f64b4cd9de05cbeea8d93d9 to understand why blank ability entries were added. Done means affected Pokémon no longer expose past ability records whose ability is null, while preserving valid historical entries.