ExpressionAttributeValues is incorrectly present when conditions are used

[terrbear]

Writing something like:

  const params = MyEntity.putParams(network, {
    conditions: [
      { attr: "PK", exists: false },
      { attr: "SK", exists: false }
    ]
  });

Results in an ExpressionAttributeValues: {}, which AWS rejects.

Workaround is to add:
delete params.ExpressionAttributeValues;

If you know they're empty.

[RavyuS]

expressionBuilder is referenced putParams (as parseConditions in Entity.js:755). It returns an empty values object by default, which is later assigned to ExpressionAttributeValues.

So exists and other functions will result in the EmptyExpressionAttributeValues error you see. My relatively primitive workaround replaces Entity.js:795 with

!isEmpty(ExpressionAttributeValues) ? { ExpressionAttributeValues } : null,

Where isEmpty is a custom function (whatever I found on google) that checks for empty objects.

Of course this is pretty dumb, but I thought of just sharing this!

[jeremydaly]

Thanks @RavyuS and @Nemo62. The pull request only fixed put, but the same issue was possible with the delete method as well. I've added a fix that puts an isEmpty function in the utils and then uses that to check the parameters when they are assembled. Thanks for everyone's input on this!