fix rubycop issue:

- don't introduce global variable
 - don't prefix getter with get_
 - single quotes instead of doubles for hash usage

lib/tiss/tiss_crawler.rb

@@ -1,24 +1,25 @@
 class TissCrawler
-
   require 'httparty'
 
-  $host = 'https://tiss.tuwien.ac.at'
+  def self.host
+    'https://tiss.tuwien.ac.at'
+  end
 
   def self.search(params)
     api = params[:api]
     search_parameter = params[:search_parameter]
     search_term = params[:search_term].parameterize(separator: '+')
-    url = $host + api + '?' + search_parameter + '=' + search_term
+    url = host + api + '?' + search_parameter + '=' + search_term
     puts(url)
 
     response = HTTParty.get(url)
-    JSON.parse(response.body)["results"]
+    JSON.parse(response.body)['results']
   end
 
   def self.get_details(params)
     api = params[:api]
     id = params[:tiss_id]
-    url = $host + api + id
+    url = host + api + id
     puts(url)
 
     response = HTTParty.get(url)
@@ -29,7 +30,7 @@ class TissCrawler
     api = params[:api]
     number = params[:number]
     semester = params[:semester]
-    url = $host + api + number + '-' + semester
+    url = host + api + number + '-' + semester
     puts(url)
 
     response = HTTParty.get(url)
@@ -39,7 +40,7 @@ class TissCrawler
   def self.get_thesis_details(params)
     api = params[:api]
     id = params[:id]
-    url = $host + api + id
+    url = host + api + id
     puts(url)
 
     response = HTTParty.get(url)
@@ -49,26 +50,24 @@ class TissCrawler
   def self.get_project_details(params)
     api = params[:api]
     id = params[:id]
-    url = $host + api + id
+    url = host + api + id
     puts(url)
 
     response = HTTParty.get(url)
     response.parsed_response['tuVienna']['project']
   end
 
-  def self.get_host
-    $host
-  end
-
   def self.get_oid_name(item)
     # Fetches a person's name based on the org id
     # Example: https://tiss.tuwien.ac.at/api/person/v22/oid/250197
     api = '/api/person/v22/oid/'
-    url = $host + api + item
+    url = host + api + item
     puts(url)
 
     response = HTTParty.get(url)
-    response.parsed_response['first_name'] + ' ' + response.parsed_response['last_name']
-  end
+    parsed_response = response.parsed_response
 
-end
+    parsed_response['error'] ||
+      parsed_response['first_name'] + ' ' + response.parsed_response['last_name']
+  end
+end