fix(stemming): handle empty dictionary retrieval gracefully

- add fallback response for empty dictionary retrieval in `StemmingDictionaries`
- refactor test setup to ensure proper test isolation
- fix webmock configuration in tests

Author: tharropoulos

lib/typesense/stemming_dictionaries.rb

@@ -32,7 +32,8 @@ def upsert(dict_id, words_and_roots_combinations)
     end
 
     def retrieve
-      @api_call.get(endpoint_path)
+      response = @api_call.get(endpoint_path)
+      response || { 'dictionaries' => [] }
     end
 
     def [](dict_id)

spec/typesense/stemming_spec.rb

@@ -19,8 +19,15 @@
     ]
   end
 
-  before { WebMock.disable! }
-  after { WebMock.enable! }
+  before do
+    WebMock.disable!
+    # Create the dictionary at the start of each test
+    client.stemming.dictionaries.upsert(dictionary_id, dictionary)
+  end
+
+  after do
+    WebMock.enable!
+  end
 
   it 'can upsert a dictionary' do
     response = client.stemming.dictionaries.upsert(dictionary_id, dictionary)