Minor clean up (improve Codacy score)

Author: devgianlu

core/src/main/java/xyz/gianlu/librespot/core/ZeroconfServer.java

@@ -152,7 +152,7 @@ private ZeroconfServer(Session.Inner inner, Configuration conf) throws IOExcepti
     @NotNull
     public static String getUsefulHostname() throws UnknownHostException {
         String host = InetAddress.getLocalHost().getHostName();
-        if (host.equals("localhost")) {
+        if (Objects.equals(host, "localhost")) {
             host = Base64.getEncoder().encodeToString(BigInteger.valueOf(ThreadLocalRandom.current().nextLong()).toByteArray()) + ".local";
             LOGGER.warn("Hostname cannot be `localhost`, temporary hostname: " + host);
             return host;

core/src/main/java/xyz/gianlu/librespot/mercury/MercuryRequests.java

@@ -4,7 +4,6 @@
 import com.google.gson.JsonObject;
 import com.spotify.metadata.proto.Metadata;
 import com.spotify.playlist4.proto.Playlist4ApiProto;
-import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import spotify.player.proto.ContextPageOuterClass;
@@ -99,14 +98,7 @@ public static JsonMercuryRequest<KeymasterToken> requestToken(@NotNull String de
     @NotNull
     private static String getAsString(@NotNull JsonObject obj, @NotNull String key) {
         JsonElement elm = obj.get(key);
-        if (elm == null) throw new NullPointerException("Unexpected null value for " + key);
-        else return elm.getAsString();
-    }
-
-    @Contract("_, _, !null -> !null")
-    private static String getAsString(@NotNull JsonObject obj, @NotNull String key, @Nullable String fallback) {
-        JsonElement elm = obj.get(key);
-        if (elm == null) return fallback;
+        if (elm == null) throw new IllegalArgumentException("Unexpected null value for " + key);
         else return elm.getAsString();
     }
 

core/src/main/java/xyz/gianlu/librespot/player/feeders/storage/AudioFileStreaming.java

@@ -148,6 +148,7 @@ public void writeChunk(byte[] buffer, int chunkIndex, boolean cached) throws IOE
 
     @Override
     public void writeHeader(byte id, byte[] bytes, boolean cached) {
+        // Not interested
     }
 
     @Override