Handle case where data to be highlighted is None, and minor refactoring (#156)
Handle case where data to be highlighted is None, and minor refactoring (#156)

* Serializers: handle case where data to be highlighted is None

 Handle case where data of the field to be highlighted is None,
 causing highlight method to fail since it expects data to of string type.

* Serializers: take out extraction of terms from request into a separate method

Taking out the extraction of terms from request into a method of its own,
namely get_terms so that its easier to override it with a custom implementation,
adds to separation of concerns.
inonit/drf-haystack