Adding a custom provider fails with error: "set_formatter() takes exactly 3 arguments (2 given)"

When I run the following code, I'm facing some difficulty. Calling the `Add Provider` keyword requires two arguments, instead of the expected 1: name of the module. This seems to me to be correct.

Assuming it might be the FakerLibrary I retrieved it's library instance and provided it to the keyword. Sadly this doesn't provide me with the desired end result but instead generates the error: "`FAIL : TypeError: set_formatter() takes exactly 3 arguments (2 given)`".

The Robot Script for this example.
```
*** Settings ***
Library FakerLibrary
*** Test Cases ***
Faker Custom Provider Generate Data

${fakerLib} Get Library Instance FakerLibrary
Add Provider ${fakerLib} OceanProvider
```
The custom provider Python code:

```
from faker.providers import BaseProvider

class OceanProvider(BaseProvider):

__provider__ = "ocean"
__lang__ = "en_US"

oceans = [
u'Atlantic', u'Pacific', u'Indian', u'Arctic', u'Southern',
]

@classmethod
def ocean(cls):
return cls.random_element(cls.oceans)
```

Start with the Robot Framework example in the issue and trace the Add Provider keyword, especially how it uses the FakerLibrary instance and OceanProvider. Reproduce the set_formatter() TypeError, then verify that the custom provider can be added with the documented one-module-name call and generate data successfully.

Written by the indexing model from the issue text.