Fixes #4948 - Trigger Condition "contains not" doesn't work correct if "nil" is stored in the user object

lib/selector/sql.rb

@@ -464,7 +464,9 @@ class Selector::Sql < Selector::Base
       query << "#{attribute} #{like} (?)"
       bind_params.push "%#{SqlHelper.quote_like(block_condition[:value])}%"
     elsif block_condition[:operator] == 'contains not'
-      query << "#{attribute} NOT #{like} (?)"
+      # NOT LIKE is always false on NULL values
+      # https://github.com/zammad/zammad/issues/4948
+      query << "#{attribute} NOT #{like} (?) OR #{attribute} IS NULL"
       bind_params.push "%#{SqlHelper.quote_like(block_condition[:value])}%"
     elsif block_condition[:operator] == 'matches regex'
       query << sql_helper.regex_match(attribute, negated: false)

spec/lib/selector/sql_spec.rb

@@ -352,6 +352,25 @@ RSpec.describe Selector::Sql do
 
           include_examples 'finds the ticket'
         end
+
+        context 'with empty-looking values in DB' do
+          let(:value) { 'Some' }
+          let(:name)  { 'ticket.note' }
+
+          before { ticket.update! note: database_value }
+
+          context 'when value is empty string' do
+            let(:database_value) { '' }
+
+            include_examples 'finds the ticket'
+          end
+
+          context 'when value is NULL' do
+            let(:database_value) { nil }
+
+            include_examples 'finds the ticket'
+          end
+        end
       end
 
       describe "operator 'is'" do