Do not override the container if it's missing from policy config

PiperOrigin-RevId: 653289605

Author: l46kok

policy/src/main/java/dev/cel/policy/CelPolicyConfig.java

@@ -127,6 +127,10 @@ public Cel extend(Cel cel, CelOptions celOptions) throws CelPolicyValidationExce
                       .map(f -> f.toCelFunctionDecl(celTypeProvider))
                       .collect(toImmutableList()));
 
+      if (!container().isEmpty()) {
+        celBuilder.setContainer(container());
+      }
+
       addAllExtensions(celBuilder, celOptions);
 
       return celBuilder.build();