MongoDB v5... ingest of public business data. I need to do a titleCase() of the $name field. Works great to about 400,000 records, then errors

I end up having anywhere from 1.5Million to 3Million documents in the collection. Ingest is from public Government CSV data aggregated to gov_data.businesses collection. Everything is ALLCAPS. I aggregated the data to a new collection with the address.city and name fields $toLower. Now I need to titleCase those fields. using address.city instead of name in the following code takes a while (28 minutes), but succeeds. name however fails with TypeError: Cannot read properties of undefined (reading 'toUpperCase') after some 400,000 documents at about 8 (minutes). Feels like a data size issue, but I've no idea. I'm relatively new to aggregations and coding in mongo/mongosh.

I borrowed the script from here: https://stackoverflow.com/questions/63113037/how-to-update-field-value-to-tittlecase-in-mongodb

use gov_data
function titleCase(str) {
    return str && str.toLowerCase().split(/\s/).map(function(word) {
        return word.replace(word[0], word[0].toUpperCase());
    }).join(' ');
}
    console.log(titleCase(undefined));
    console.log(titleCase(""));
    console.log(titleCase(null));
    console.log(titleCase("NAMAR"));
db.businesses.aggregate().forEach(function(doc){
    db.businesses.bulkWrite(
        { "_id": doc._id },
        { "$set": { "name": titleCase(doc.name) } }
    );
});

You might have a document starting with a space or with consecutive space in it. The split function will resolve to an array like [ '', 'toto' ] and the empty char has no toUpperCase function.

You should update your titleCase function to fix this.
You could do as follows (warning it will remove the extra spaces):

function titleCase(str) {
    return str && str.toLowerCase().split(/\s/).reduce(function(element,word) {
        if (word.length>0){
        element.push(word.replace(word[0], word[0].toUpperCase()));
        }
        return element;
    }, []
    ).join(' ');
}

This should fix your issue.

On top of that, you should consider using the updateMany function to update all document instead of iterating with forEach.

db.businesses.updateMany(
        {},
        [{ "$set": { "name": titleCase("$name") } }]
    );
});