Repository: helidon-io/helidon
Issue: Regression in JsonSupport

Reading content as JsonObject fails in 0.11.1, works in 0.11.0

```
request.content()
                .as(JsonObject.class)
                .thenAccept(json -> {
                    // this line is never reached
                    greeting.set(json.getString("greeting"));
                    sendGreeting(response);
                });
```

## Environment Details
* Helidon Version: 0.11.1
* Helidon SE
* JDK version: 1.8
* OS: Mac

----------

When I upgrade to 0.11.1 (and change JsonSupport to new package), the PUT request never reaches the line that processes the JsonObject.
Downgrading to 0.11.0 (and changing the JsonSupport to old package), the PUT request works just fine.

Registration:
```
return Routing.builder()
                .register(JsonSupport.create())
                //.register("/greet", new GreetService(greeting, config))
                .register("/greeting", new GreetingService(greeting))
                .build();
```

GreetingService:
```
/*
 * Copyright (c) 2019 Oracle and/or its affiliates. All rights reserved.
 */
package io.helidon.examples.screencast.se;

import java.util.Collections;
import java.util.concurrent.atomic.AtomicReference;

import javax.json.Json;
import javax.json.JsonBuilderFactory;
import javax.json.JsonObject;

import io.helidon.webserver.Routing;
import io.helidon.webserver.ServerRequest;
import io.helidon.webserver.ServerResponse;
import io.helidon.webserver.Service;

/**
 * Greeting management.
 */
public class GreetingService implements Service {
    private static final JsonBuilderFactory JSON = Json.createBuilderFactory(Collections.emptyMap());

    private final AtomicReference<String> greeting;

    public GreetingService(AtomicReference<String> greeting) {
        this.greeting = greeting;
    }

    @Override
    public void update(Routing.Rules rules) {
        rules.put("/", this::updateGreetingHandler);
    }

    private void greetingHandler(ServerRequest request, ServerResponse response) {
        sendGreeting(response);
    }

    private void updateGreetingHandler(ServerRequest request, ServerResponse response) {
        request.content()
                .as(JsonObject.class)
                .thenAccept(json -> {
                    greeting.set(json.getString("greeting"));
                    sendGreeting(response);
                });
    }

    private void sendGreeting(ServerResponse response) {
        response.send(JSON.createObjectBuilder()
                              .add("greeting", greeting.get())
                              .build());
    }
}
```

Changed files:
media/jsonp/server/src/main/java/io/helidon/media/jsonp/server/JsonSupport.java

diff --git a/media/jsonp/server/src/main/java/io/helidon/media/jsonp/server/JsonSupport.java b/media/jsonp/server/src/main/java/io/helidon/media/jsonp/server/JsonSupport.java
index 2d9bd36777..a0d2f69d43 100644
--- a/media/jsonp/server/src/main/java/io/helidon/media/jsonp/server/JsonSupport.java
+++ b/media/jsonp/server/src/main/java/io/helidon/media/jsonp/server/JsonSupport.java
@@ -18,6 +18,7 @@ package io.helidon.media.jsonp.server;
 
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.List;
 import java.util.Objects;
 import java.util.function.Function;
@@ -185,7 +186,7 @@ public final class JsonSupport implements Service, Handler {
      * Returns a charset from {@code Content-Type} header parameter or {@code null} if not defined.
      *
      * @param headers parameters representing request or response headers
-     * @return a charset or {@code null}
+     * @return a charset or {@code UTF-8} as default
      * @throws RuntimeException if charset is not supported
      */
     private Charset determineCharset(Parameters headers) {
@@ -199,7 +200,7 @@ public final class JsonSupport implements Service, Handler {
                         return null; // Do not need default charset. Can use JSON specification.
                     }
                 })
-                .orElse(null);
+                .orElse(StandardCharsets.UTF_8);
     }
 
     /**