Cannot change player skins

I am trying to change the skin of players for a minigame I have. However, the code does not return any errors, but It also doesn't function.

Code:

    public boolean setSkin(UUID uuid) {
        try {
            HttpsURLConnection connection = (HttpsURLConnection) new URL(String.format("https://sessionserver.mojang.com/session/minecraft/profile/%s?unsigned=false", UUIDTypeAdapter.fromUUID(uuid))).openConnection();
            if (connection.getResponseCode() == HttpsURLConnection.HTTP_OK) {

                String[] values = new BufferedReader(new InputStreamReader(connection.getInputStream())).lines().filter(x -> (x.contains("value") || x.contains("signature"))).collect(Collectors.toList()).toString().split("\"");

                ((CraftPlayer) player).getHandle().getProfile().getProperties().put("textures", new Property("textures", values[3], values[7]));
                return true;
            } else {
                System.out.println("Connection could not be opened (Response code " + connection.getResponseCode() + ", " + connection.getResponseMessage() + ")");
                return false;
            }
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }
    }

When debugging, I made sure that values[3] and values[7] corresponded to the correct values, or in other words the texture value & the signature. The boolean returns true.

I am running the server on bukkit 1.8.3. Is there anything I am missing from this block of code?

UPDATE:

Code:

[16:21:02 WARN]: An exception was thrown by a user handler's exceptionCaught() method while handling the following exception:
java.lang.NullPointerException
        at net.minecraft.server.v1_8_R3.NetworkManager.close(NetworkManager.java:245) ~[server.jar:git-Spigot-db6de12-18fbb24]
        at net.minecraft.server.v1_8_R3.NetworkManager.channelInactive(NetworkManager.java:105) ~[server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:233) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:219) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:228) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:233) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:219) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:228) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:233) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:219) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:233) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:219) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.handler.timeout.ReadTimeoutHandler.channelInactive(ReadTimeoutHandler.java:144) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:233) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:219) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:769) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.AbstractChannel$AbstractUnsafe$5.run(AbstractChannel.java:567) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:380) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:357) [server.jar:git-Spigot-db6de12-18fbb24]
        at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116) [server.jar:git-Spigot-db6de12-18fbb24]
        at java.base/java.lang.Thread.run(Thread.java:832) [?:?]

This error is thrown after I attempt to change my skin a couple of times, then log off. When I try to connect back, I get immediately disconnected, and the server does not show up as online on my list.

 

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