When 'index' attribute in fields are shown when retrieving mapping?

I noticed that even if I set { "index": "not_analyzed" } for certain types of fields, like for instance integer, it apparently ignores, because when I fetch the mapping for the given index/type, such attribute doesn't come together with the given field.

That is obvious, given analyzing integer fields doesn't make sense at all.
So my question is: should I consider only "string" fields to bring such "index" attribute when retrieving mappings from the server? So, considering the existing core types, should I consider the types integer/long, float/double and boolean as types where the "index" attribute doesn't apply to?

This should be applied, it might help if we can see your overall mapping.

But it turns out it doesn't apply. If the field is of type integer, for instance, and the index attribute is not_analyzed it doesn't even get registered in the mapping. At least if I retrieve the type mapping the index attribute doesn't come along within the field.