Yield no results for blank searches on User name, username and email

Given no search term, the `search` and `search_with_secondary_emails` methods will yield an empty result set

app/models/user.rb

@@ -318,6 +318,8 @@ class User < ActiveRecord::Base
     #
     # Returns an ActiveRecord::Relation.
     def search(query)
+      return none if query.blank?
+
       query = query.downcase
       order = <<~SQL
@@ -341,6 +343,8 @@ class User < ActiveRecord::Base
     # This method uses ILIKE on PostgreSQL and LIKE on MySQL.
     def search_with_secondary_emails(query)
+      return none if query.blank?
+
       query = query.downcase
       email_table = Email.arel_table

spec/models/user_spec.rb

@@ -966,6 +966,14 @@ describe User do
         expect(described_class.search(user3.username.upcase)).to eq([user3])
       end
     end
+
+    it 'returns no matches for an empty string' do
+      expect(described_class.search('')).to be_empty
+    end
+
+    it 'returns no matches for nil' do
+      expect(described_class.search(nil)).to be_empty
+    end
   end
   describe '.search_with_secondary_emails' do
@@ -1020,6 +1028,14 @@ describe User do
     it 'does not return users with a matching part of secondary email' do
       expect(search_with_secondary_emails(email.email[1..4])).not_to include([email.user])
     end
+
+    it 'returns no matches for an empty string' do
+      expect(search_with_secondary_emails('')).to be_empty
+    end
+
+    it 'returns no matches for nil' do
+      expect(search_with_secondary_emails(nil)).to be_empty
+    end
   end
   describe '.find_by_ssh_key_id' do