Fix: validate trace id (#2749)

Author: robertino

gems/aws-sdk-core/CHANGELOG.md

@@ -1,6 +1,8 @@
 Unreleased Changes
 ------------------
 
+* Issue - Fix errors in recursion detection when `_X_AMZN_TRACE_ID` is unset (#2748).
+
 3.136.0 (2022-08-25)
 ------------------
 

gems/aws-sdk-core/lib/aws-sdk-core/plugins/recursion_detection.rb

@@ -20,6 +20,8 @@ def call(context)
 
         private
         def validate_header(header_value)
+          return unless header_value
+
           if (header_value.chars & (0..31).map(&:chr)).any?
             raise ArgumentError, 'Invalid _X_AMZN_TRACE_ID value: '\
               'contains ASCII control characters'

gems/aws-sdk-core/spec/aws/plugins/recursion_detection_spec.rb

@@ -99,6 +99,15 @@ module Plugins
             end
           end
         end
+
+        context 'X_AMZ_TRACE_ID is unset' do
+          let(:env_trace_id) { nil }
+
+          it 'does not set the header' do
+            resp = client.operation_with_trace_id
+            expect(resp.context.http_request.headers['x-amzn-trace-id']).to be_nil
+          end
+        end
       end
     end
   end