fix warnings

Author: mythz

lib/converters/duration_converter.dart

@@ -20,7 +20,7 @@ class DurationConverter implements IConverter
     var hasTime = t.length == 2;
     var d = splitOnFirst(t[0], 'D');
     if (d.length == 2) {
-      var day = int.parse(d[0], onError: (s) => null);
+      var day = int.tryParse(d[0]) ?? null;
       if (day != null) {
         days = day;
       }
@@ -29,23 +29,23 @@ class DurationConverter implements IConverter
     if (hasTime) {
       var h = splitOnFirst(t[1], 'H');
       if (h.length == 2) {
-        var hour = int.parse(h[0], onError: (s) => null);
+        var hour = int.tryParse(h[0]) ?? null;
         if (hour != null) {
           hours = hour;
         }
       }
 
       var m = splitOnFirst(h[h.length - 1], 'M');
       if (m.length == 2) {
-        var min = int.parse(m[0], onError: (s) => null);
+        var min = int.tryParse(m[0]) ?? null;
         if (min != null) {
           minutes = min;
         }
       }
 
       var s = splitOnFirst(m[m.length - 1], 'S');
       if (s.length == 2) {
-        var millis = double.parse(s[0], (s) => null);
+        var millis = double.tryParse(s[0]) ?? null;
         if (millis != null) {
           ms = millis;
         }

lib/json_service_client.dart

@@ -78,7 +78,7 @@ class JsonServiceClient implements IServiceClient {
     replyBaseUrl = combinePaths([baseUrl, "json", "reply"]) + "/";
     oneWayBaseUrl = combinePaths([baseUrl, "json", "oneway"]) + "/";
     headers = {
-      HttpHeaders.ACCEPT: "application/json",
+      HttpHeaders.acceptHeader: "application/json",
     };
     client = new HttpClient();
     cookies = new List<Cookie>();
@@ -363,16 +363,16 @@ class JsonServiceClient implements IServiceClient {
     var req = await client.openUrl(method, info.uri ?? createUri(url));
 
     if (bearerToken != null)
-      req.headers.add(HttpHeaders.AUTHORIZATION, 'Bearer ' + bearerToken);
+      req.headers.add(HttpHeaders.authorizationHeader, 'Bearer ' + bearerToken);
     else if (userName != null)
-      req.headers.add(HttpHeaders.AUTHORIZATION,
+      req.headers.add(HttpHeaders.authorizationHeader,
           'Basic ' + base64.encode(utf8.encode('$userName:$password')));
 
     req.cookies.addAll(this.cookies);
 
     req.headers.chunkedTransferEncoding = false;
     headers.forEach((key, val) {
-      if (key == HttpHeaders.CONTENT_TYPE) {
+      if (key == HttpHeaders.contentTypeHeader) {
         var parts = val.split("/");
         req.headers.contentType = new ContentType(parts[0], parts[1]);
       } else {
@@ -381,7 +381,7 @@ class JsonServiceClient implements IServiceClient {
     });
 
     if (bodyStr != null) {
-      req.headers.contentType = ContentType.JSON;
+      req.headers.contentType = ContentType.json;
       req.contentLength = bodyStr.length;
     }