diff --git a/lib/rack/tracker/google_global/google_global.rb b/lib/rack/tracker/google_global/google_global.rb
index 0631794..5ccb817 100644
--- a/lib/rack/tracker/google_global/google_global.rb
+++ b/lib/rack/tracker/google_global/google_global.rb
@@ -35,9 +35,7 @@ def events
   end
 
   def trackers
-    options[:trackers].map { |tracker|
-      tracker[:id].respond_to?(:call) ? tracker.merge(id: tracker[:id].call(env)) : tracker
-    }.reject { |tracker| tracker[:id].nil? }
+    @_trackers ||= build_trackers
   end
 
   def set_options
@@ -46,6 +44,31 @@ def set_options
 
   private
 
+  def build_trackers
+    options[:trackers].map(&method(:call_tracker)).reject(&method(:invalid_tracker?))
+  end
+
+  def call_tracker(tracker)
+    if tracker[:id].respond_to?(:call)
+      tracker.merge(id: tracker[:id].call(env))
+    else
+      tracker
+    end
+  end
+
+  def invalid_tracker?(tracker)
+    if tracker[:id].to_s.strip == ''
+      $stdout.puts <<~WARN
+      WARNING: One of the trackers specified for Rack::Tracker handler 'google_global' is empty.
+               Trackers: #{options[:trackers]}
+      WARN
+
+      true
+    else
+      false
+    end
+  end
+
   def build_set_options
     value = options[:set]
     value.respond_to?(:call) ? value.call(env) : value
diff --git a/lib/rack/tracker/google_global/template/google_global.erb b/lib/rack/tracker/google_global/template/google_global.erb
index b6141a8..9103419 100644
--- a/lib/rack/tracker/google_global/template/google_global.erb
+++ b/lib/rack/tracker/google_global/template/google_global.erb
@@ -1,4 +1,4 @@
-<% if trackers %>
+<% if trackers.any? %>
 <script async src='https://www.googletagmanager.com/gtag/js?id=<%= trackers[0][:id] %>'></script>
 <script>
   window.dataLayer = window.dataLayer || [];
diff --git a/spec/integration/google_global_integration_spec.rb b/spec/integration/google_global_integration_spec.rb
index 7079036..14df465 100644
--- a/spec/integration/google_global_integration_spec.rb
+++ b/spec/integration/google_global_integration_spec.rb
@@ -3,28 +3,39 @@
 RSpec.describe "Google Global Integration Integration" do
   before do
     setup_app(action: :google_global) do |tracker|
-      tracker.handler :google_global, trackers: [{ id: 'U-XXX-Y' }]
+      tracker.handler :google_global, tracker_options
     end
     visit '/'
   end
 
-  subject { page }
+  let(:tracker_options) { { trackers: [{ id: 'U-XXX-Y' }] } }
 
   it "embeds the script tag with tracking event from the controller action" do
     expect(page.find("head")).to have_content('U-XXX-Y')
   end
 
   describe 'adjust tracker position via options' do
-    before do
-      setup_app(action: :google_global) do |tracker|
-        tracker.handler :google_global, trackers: [{ id: 'U-XXX-Y' }], position: :body
-      end
-      visit '/'
-    end
+    let(:tracker_options) { { trackers: [{ id: 'U-XXX-Y' }], position: :body } }
 
     it "will be placed in the specified tag" do
      expect(page.find("head")).to_not have_content('U-XXX-Y')
      expect(page.find("body")).to have_content('U-XXX-Y')
     end
   end
+
+  describe "handles empty tracker id" do
+    let(:tracker_options) { { trackers: [{ id: nil }, { id: "" }, { id: "  " }] } }
+
+    it "does not inject scripts" do
+      expect(page.find("head")).to_not have_content("<script async src='https://www.googletagmanager.com/gtag/js?id=")
+    end
+  end
+
+  describe "callable tracker id" do
+    let(:tracker_options) { { trackers: [{ id: proc { "U-XXX-Y" } }] } }
+
+    it "is injected into head with id from proc" do
+      expect(page.find("head")).to have_content('U-XXX-Y')
+    end
+  end
 end