SSL handshake exception

//Message

$$fixit >>> customcommands >>> sendFileURL >>> https://my.mixtape.moe/ypzgwd.png

//Error
11:47:43.006 [GuildCreateGroup-Thread-5] ERROR javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
        at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
        at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1949)
        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:302)
        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:296)
        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1497)
        at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:212)
        at sun.security.ssl.Handshaker.processLoop(Handshaker.java:979)
        at sun.security.ssl.Handshaker.process_record(Handshaker.java:914)
        at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1062)
        at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1375)
        at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1403)
        at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1387)
        at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:563)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1512)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1440)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
        at com.github.vaerys.main.Utility.sendFileURL(Utility.java:297)
        at com.github.vaerys.handlers.CCHandler.handleCommand(CCHandler.java:133)
        at com.github.vaerys.handlers.CCHandler.<init>(CCHandler.java:52)
        at com.github.vaerys.handlers.MessageHandler.<init>(MessageHandler.java:43)
        at com.github.vaerys.main.AnnotationListener.onMessageReceivedEvent(AnnotationListener.java:77)
        at sx.blah.discord.api.events.EventDispatcher$MethodEventHandler.handle(EventDispatcher.java:723)
        at sx.blah.discord.api.events.EventDispatcher.lambda$null$19(EventDispatcher.java:653)
        at sx.blah.discord.api.events.EventDispatcher$$Lambda$48/921814994.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
        at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:387)
        at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
        at sun.security.validator.Validator.validate(Validator.java:260)
        at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
        at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
        at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1479)
        ... 23 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
        at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:145)
        at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:131)
        at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
        at sun.security.validator.P

//Code
public static IMessage sendFileURL(String message, String imageURL, IChannel channel, boolean loadMessage) {
        IMessage toDelete = null;
        if (loadMessage) {
            toDelete = sendMessage("`Loading...`", channel).get();
        }
        IMessage sentMessage = null;
        try {
            //setup for the stream
            final HttpURLConnection connection = (HttpURLConnection) new URL(imageURL).openConnection();
            connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_5) " + "AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.65 Safari/537.31");
            InputStream stream = connection.getInputStream();
            sentMessage = (IMessage) XRequestBuffer.request(() -> {
                try {
                    //set up the file name
                    URL url = new URL(imageURL);
                    String filename = FilenameUtils.getName(url.getPath());
                    if (filename.equalsIgnoreCase("giphy.gif")) {
                        return sendMessage(message + " " + imageURL, channel).get();
                    }
                    //checks if url is valid
                    if (!isImageLink(filename)) {
                        return sendMessage(message + " " + imageURL, channel).get();
                    }
                    //sends message/files
                    if (StringUtils.containsOnly(message, "\n") || (message == null) || message.equals("") && imageURL != null) {
                        return channel.sendFile("", stream, filename);
                    } else if (message != null && !message.isEmpty() && imageURL != null) {
                        return channel.sendFile(removeMentions(message), false, stream, filename);
                    } else {
                        logger.debug("Error sending File to channel with id: " + channel.getStringID() + " on guild with id: " + channel.getGuild().getStringID() +
                                ".\n" + Constants.PREFIX_EDT_LOGGER_INDENT + "Reason: No file to send");
                        return null;
                    }
                } catch (DiscordException e) {
                    if (e.getMessage().contains("CloudFlare")) {
                        return sendFileURL(message, imageURL, channel, false);
                    } else {
                        sendStack(e);
                        return null;
                    }
                } catch (MalformedURLException e) {
                    return sendMessage(message + " " + imageURL, channel).get();
                } catch (IOException e) {
                    sendStack(e);
                    return null;
                } catch (MissingPermissionsException e) {
                    logger.debug("Error sending File to channel with id: " + channel.getStringID() + " on guild with id: " + channel.getGuild().getStringID() +
                            ".\n" + Constants.PREFIX_EDT_LOGGER_INDENT + "Reason: Missing permissions.");
                    return sendMessage(message + " <" + imageURL + ">", channel).get();
                }
            }).get();
            stream.close();
        } catch (MalformedURLException e) {
            sendStack(e);
        } catch (IOException e) {
            sendStack(e);
        }
        if (loadMessage && toDelete != null) {
            deleteMessage(toDelete);
        }
        return sentMessage;
    }