config: RawConfig merge should only set unknown keys non-nil if

non-empty

config/raw_config.go

@@ -191,6 +191,7 @@ func (r *RawConfig) Merge(other *RawConfig) *RawConfig {
 	}
 
 	// Build the unknown keys
+	if len(r.unknownKeys) > 0 || len(other.unknownKeys) > 0 {
 		unknownKeys := make(map[string]struct{})
 		for _, k := range r.unknownKeys {
 			unknownKeys[k] = struct{}{}
@@ -203,6 +204,7 @@ func (r *RawConfig) Merge(other *RawConfig) *RawConfig {
 		for k, _ := range unknownKeys {
 			result.unknownKeys = append(result.unknownKeys, k)
 		}
+	}
 
 	return result
 }