add easy csp header config removal

.rubocop.yml

@@ -44,8 +44,8 @@ Metrics/ParameterLists:
   Max: 7
 
 Metrics/ClassLength:
-  Max: 300
+  Max: 350
 
 Metrics/ModuleLength:
-  Max: 300
+  Max: 350
 

lib/rackr.rb

@@ -7,7 +7,7 @@
 
 # Rackr is a simple router for Rack.
 class Rackr
-  VERSION = '0.0.70'
+  VERSION = '0.0.71'
 
   class NotFound < StandardError; end
 

lib/rackr/action.rb

@@ -342,6 +342,7 @@ def content_security_policy
           @content_security_policy ||=
             DEFAULT_CSP_HEADERS
             .merge(config&.dig(:csp_headers) || {})
+            .compact
             .map { |k, v| "#{k.to_s.tr('_', '-')} #{v}" }
             .join('; ')
         end

lib/spec/rackr/action_spec.rb

@@ -510,6 +510,32 @@ class SomeClass2
       end
     end
 
+    context 'when removing csp_headers' do
+      let(:config) do
+        {
+          csp_headers: {
+            style_src: nil,
+          }
+        }
+      end
+
+      let(:expected_csp) do
+        default = {
+          base_uri: "'self'", child_src: "'self'", connect_src: "'self'",
+          default_src: "'none'", font_src: "'self'", form_action: "'self'",
+          frame_ancestors: "'self'", frame_src: "'self'",
+          img_src: "'self' https: data:", media_src: "'self'",
+          object_src: "'none'", script_src: "'self'",
+        }
+        default.map { |k, v| "#{k.to_s.tr('_', '-')} #{v}" }.join('; ')
+      end
+
+      it 'merges and overrides the default csp' do
+        result = subject.render(html: 'test')
+        expect(result[1]['content-security-policy']).to eq(expected_csp)
+      end
+    end
+
     context 'with user-defined csp_headers' do
       let(:config) do
         {