Fix empty query parameters in expand_parameters method

Before, there was no distinction between empty parameters passed to the
backend. For example, for this query string: `?expand`

The query parameter string was parsed into `params` (by Rails), and
later on, translated into a query parameter string with the method
`.to_query`. This lead to passing empty query parameters adding an `=`
sign in the end. For example: `?expand=`.

That make the backend throw a 400 error with a boolean value not
recognized.

This commit, split the query parameters in empty and non-empty, solving
this issue.

Author: eduardoj

src/api/app/lib/backend/connection_helper.rb

@@ -114,8 +114,13 @@ def expand_params(params, expand)
 
         expanded_params += params.delete(key).map { |value| value.to_query(key) } if params.key?(key)
       end
-      expanded_params += [params.to_query] unless params.empty?
-      expanded_params
+
+      empty_query_parameters = params.select { |_, v| v.nil? }
+      expanded_params += [empty_query_parameters.keys.join('&')]
+
+      expanded_params += [params.except(*empty_query_parameters.keys).to_query]
+
+      expanded_params.compact_blank
     end
 
     def calculate_endpoint(endpoint)