Ensure no empty sentinels list is allowed

lib/3scale/backend/storage_helpers.rb

@@ -216,11 +216,11 @@ def cfg_sentinels_handler(options)
             role = options.delete :role
             sentinels = options.delete :sentinels
             # The Redis client can't accept empty string or array of :sentinels
-            return options if sentinels.nil? || sentinels.empty?
+            return options if sentinels.to_s.strip.empty? || sentinels.empty?
 
             sentinels = Splitter.split(sentinels) if sentinels.is_a? String
 
-            options[:sentinels] = sentinels.map do |sentinel|
+            sentinels = sentinels.map do |sentinel|
               if sentinel.is_a? Hash
                 next if sentinel.empty?
                 sentinel.fetch(:host) do
@@ -233,6 +233,10 @@ def cfg_sentinels_handler(options)
               end
             end.compact
 
+            return options if sentinels.empty?
+
+            options[:sentinels] = sentinels
+
             # For the sentinels that do not have the :port key or
             # the port key is nil we configure them with the default
             # sentinel port

test/unit/storage_async_test.rb

@@ -165,7 +165,7 @@ def test_role_empty_when_sentinels_does_not_exist
   end
 
   def test_sentinels_empty
-    ['', []].each do |sentinels_val|
+    [nil, '', ' ', [], [nil], [''], [' '], [{}]].each do |sentinels_val|
       config_obj = {
         url: 'redis://master-group-name',
         sentinels: sentinels_val

test/unit/storage_sync_test.rb

@@ -225,7 +225,7 @@ def test_role_empty_when_sentinels_does_not_exist
   end
 
   def test_sentinels_empty
-    ['', []].each do |sentinels_val|
+    [nil, '', ' ', [], [nil], [''], [' '], [{}]].each do |sentinels_val|
       config_obj = {
         url: 'redis://master-group-name',
         sentinels: sentinels_val