fix: arguments merge function

[fpdrozd]

This PR fixes the filter of empty objects and adds a filter for objects with falsy props to the squashAndPreparePositionalArguments function. The lack of them caused an error when calling the account.completedOrder endpoint. When provided with the following array:

[
  { order_number: undefined },
  {
    bearer_token: '...',
    order_number: 'R285427148',
    include: '...'
  },
  {}
]

The merge function would overwrite order_number to undefined instead of assigning the valid R285427148.

This might have possibly caused similar errors in other endpoints that use the new SDK's options interface.