Way to log null?

[shareefer]

Hi - is there a way to log null? I noticed if I log a value of null the key/value pair does not show up. I have resorted to checking if its null and then changing the value to an empty string before logging. We deal with syncing data and need to log the before value and after value - either the before or after value can be null.

If there is no kind of flag for this, it would be cool if I could add some sort of middleware that always performs this check before logging an object.

thanks in advance

[dreamorosi]

Hi @shareefer, by default we remove null, undefined, and '', this however applies only to top-level key/value pairs. If your null value is within an object we'll log it.

For example:

import { Logger } from '@aws-lambda-powertools/logger';

const logger = new Logger();

const nullVal = null;

logger.info('some val', nullVal); // key: nullVal - value: null -> removed
logger.info('some other val', { nullVal }); // key: extra - value: null -> removed

const comparison = {
  before: true,
  after: null
};

logger.info('wrapped', { comparison }); // not removed, see below
// {"level":"INFO","message":"wrapped","timestamp":"2025-08-28T22:35:30.694Z","service":"service_undefined","sampling_rate":0,"comparison":{"before":true,"after":null}}

If your null value must be at the top level, then the only way I can't think of doing it - at least with the current feature set - requires three steps:

Extend the LogItem class and override the removeEmptyKeys method here with your logic that keeps null values:

import { LogItem } from '@aws-lambda-powertools/logger';
import type { LogAttributes } from '@aws-lambda-powertools/logger/types';

class MyLogItem extends LogItem {
  public removeEmptyKeys(attributes: LogAttributes) {
    // your logic
    return attributes;
  }
}

Then, use this LogItem in a custom LogFormatter class as documented here.

Finally, use your custom log formatter that uses the modified LogItem when you instantiate the Logger like:

import { Logger } from '@aws-lambda-powertools/logger';

const logger = new Logger({
  logFormatter: new MyLogFormatter(),
  // ... other configs
});

I realize that this is kind of verbose, so however far this is the first time we heard someone wanting to log these values at the top level.

[shareefer]

I can certainly log within an object thank you!