Review fixes for akka-http-10.0:javaagent (#16496)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>

Author: otelbot[bot]

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/client/HttpHeaderSetter.java

@@ -10,6 +10,7 @@
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.context.propagation.TextMapSetter;
+import javax.annotation.Nullable;
 
 public class HttpHeaderSetter implements TextMapSetter<HttpHeaderSetter.AkkaHttpHeaders> {
 
@@ -20,7 +21,10 @@ public HttpHeaderSetter(ContextPropagators contextPropagators) {
   }
 
   @Override
-  public void set(AkkaHttpHeaders carrier, String key, String value) {
+  public void set(@Nullable AkkaHttpHeaders carrier, String key, String value) {
+    if (carrier == null) {
+      return;
+    }
     HttpRequest request = carrier.getRequest();
     if (request != null) {
       // It looks like this cast is only needed in Java, Scala would have figured it out

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/server/AkkaFlowWrapper.java

@@ -123,7 +123,7 @@ public void onPush() {
                 context = AkkaRouteHolder.init(context);
                 tracingRequest = new TracingRequest(context, request);
               }
-              // event if span wasn't started we need to push TracingRequest to match response
+              // even if span wasn't started we need to push TracingRequest to match response
               // with request
               requests.push(tracingRequest);
 

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/server/AkkaHttpServerHeaders.java

@@ -5,6 +5,7 @@
 
 package io.opentelemetry.javaagent.instrumentation.akkahttp.server;
 
+import static java.util.Collections.emptyIterator;
 import static java.util.stream.Collectors.toList;
 
 import akka.http.javadsl.model.HttpHeader;
@@ -16,9 +17,9 @@
 import java.util.Locale;
 import java.util.Optional;
 import java.util.stream.StreamSupport;
+import javax.annotation.Nullable;
 
-enum AkkaHttpServerHeaders implements TextMapGetter<HttpRequest> {
-  INSTANCE;
+final class AkkaHttpServerHeaders implements TextMapGetter<HttpRequest> {
 
   @Override
   public Iterable<String> keys(HttpRequest httpRequest) {
@@ -28,13 +29,19 @@ public Iterable<String> keys(HttpRequest httpRequest) {
   }
 
   @Override
-  public String get(HttpRequest carrier, String key) {
+  public String get(@Nullable HttpRequest carrier, String key) {
+    if (carrier == null) {
+      return null;
+    }
     Optional<HttpHeader> header = carrier.getHeader(key);
     return header.map(HttpHeader::value).orElse(null);
   }
 
   @Override
-  public Iterator<String> getAll(HttpRequest carrier, String key) {
+  public Iterator<String> getAll(@Nullable HttpRequest carrier, String key) {
+    if (carrier == null) {
+      return emptyIterator();
+    }
     String headerName = key.toLowerCase(Locale.ROOT);
     List<String> result = new ArrayList<>();
     for (HttpHeader header : carrier.getHeaders()) {

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/server/AkkaHttpServerSingletons.java

@@ -20,7 +20,7 @@ public final class AkkaHttpServerSingletons {
         JavaagentHttpServerInstrumenters.create(
             AkkaHttpUtil.instrumentationName(),
             new AkkaHttpServerAttributesGetter(),
-            AkkaHttpServerHeaders.INSTANCE);
+            new AkkaHttpServerHeaders());
   }
 
   public static Instrumenter<HttpRequest, HttpResponse> instrumenter() {