[SCB-2554] Avoid null value for Optional Type (#3048)

diff --git a/core/src/main/java/org/apache/servicecomb/core/provider/producer/ProducerBootListener.java b/core/src/main/java/org/apache/servicecomb/core/provider/producer/ProducerBootListener.java
index 70f9ad2..5ac82a6 100644
--- a/core/src/main/java/org/apache/servicecomb/core/provider/producer/ProducerBootListener.java
+++ b/core/src/main/java/org/apache/servicecomb/core/provider/producer/ProducerBootListener.java
@@ -54,6 +54,7 @@
     for (String endpoint : microservice.getInstance().getEndpoints()) {
       if (endpoint.startsWith("rest://") && endpoint.indexOf("sslEnabled=true") > 0) {
         swaggerSchema = "https";
+        break;
       }
     }
 
diff --git a/providers/provider-springmvc/src/main/java/org/apache/servicecomb/provider/springmvc/reference/CseHttpMessageConverter.java b/providers/provider-springmvc/src/main/java/org/apache/servicecomb/provider/springmvc/reference/CseHttpMessageConverter.java
index a913d51..018abc9 100644
--- a/providers/provider-springmvc/src/main/java/org/apache/servicecomb/provider/springmvc/reference/CseHttpMessageConverter.java
+++ b/providers/provider-springmvc/src/main/java/org/apache/servicecomb/provider/springmvc/reference/CseHttpMessageConverter.java
@@ -50,8 +50,7 @@
   }
 
   @Override
-  public Object read(Class<? extends Object> clazz,
-      HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
+  public Object read(Class<?> clazz, HttpInputMessage inputMessage) throws HttpMessageNotReadableException {
     throw new IllegalStateException("not supported");
   }
 
diff --git a/swagger/swagger-generator/generator-core/src/test/java/org/apache/servicecomb/swagger/generator/core/schema/Schema.java b/swagger/swagger-generator/generator-core/src/test/java/org/apache/servicecomb/swagger/generator/core/schema/Schema.java
index 75c5807..bb8c683 100644
--- a/swagger/swagger-generator/generator-core/src/test/java/org/apache/servicecomb/swagger/generator/core/schema/Schema.java
+++ b/swagger/swagger-generator/generator-core/src/test/java/org/apache/servicecomb/swagger/generator/core/schema/Schema.java
@@ -178,7 +178,7 @@
   }
 
   public Optional<String> testOptional() {
-    return null;
+    return Optional.empty();
   }
 
   public CompletableFuture<Optional<String>> testCompletableFutureOptional() {