diff --git a/_examples/advanced-generic/_testdata/openapi.json b/_examples/advanced-generic/_testdata/openapi.json
index 8faaad0..250f48d 100644
--- a/_examples/advanced-generic/_testdata/openapi.json
+++ b/_examples/advanced-generic/_testdata/openapi.json
@@ -402,10 +402,7 @@
             },
             "content":{"text/csv":{"schema":{"type":"string"}}}
           },
-          "304":{
-            "description":"Not Modified",
-            "content":{"application/json":{"schema":{"$ref":"#/components/schemas/AdvancedCustomErr"}}}
-          },
+          "304":{"description":"Not Modified"},
           "500":{
             "description":"Internal Server Error",
             "content":{"application/json":{"schema":{"$ref":"#/components/schemas/AdvancedCustomErr"}}}
diff --git a/openapi/collector.go b/openapi/collector.go
index 2006fd0..3070c88 100644
--- a/openapi/collector.go
+++ b/openapi/collector.go
@@ -267,7 +267,10 @@ func (c *Collector) setJSONResponse(op *openapi3.Operation, output interface{},
 	oc.Operation = op
 	oc.Output = output
 	oc.HTTPStatus = statusCode
-	oc.RespContentType = c.DefaultErrorResponseContentType
+
+	if output != nil {
+		oc.RespContentType = c.DefaultErrorResponseContentType
+	}
 
 	return c.Reflector().SetupResponse(oc)
 }
@@ -295,6 +298,10 @@ func (c *Collector) processExpectedErrors(op *openapi3.Operation, u usecase.Inte
 			statusCode, errResp = rest.Err(e)
 		}
 
+		if statusCode < http.StatusOK || statusCode == http.StatusNotModified || statusCode == http.StatusNoContent {
+			errResp = nil
+		}
+
 		if errsByCode[statusCode] == nil {
 			statusCodes = append(statusCodes, statusCode)
 		}
@@ -306,6 +313,10 @@ func (c *Collector) processExpectedErrors(op *openapi3.Operation, u usecase.Inte
 		}
 	}
 
+	return c.combineErrors(op, statusCodes, errsByCode)
+}
+
+func (c *Collector) combineErrors(op *openapi3.Operation, statusCodes []int, errsByCode map[int][]interface{}) error {
 	for _, statusCode := range statusCodes {
 		var (
 			errResps = errsByCode[statusCode]