Move InstrumentationModuleInstaller creation from field initializer to extend()

InstrumentationLoader is instantiated by ServiceLoader (no-arg constructor),
at which point InstrumentationHolder.getInstrumentation() is still null.
Moving the requireNonNull + construction into extend() defers it to when
Instrumentation is guaranteed to be available, fixing the NPE.
Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/instrumentation/InstrumentationLoader.java

@@ -16,20 +16,21 @@
 import io.opentelemetry.javaagent.tooling.AgentExtension;
 import io.opentelemetry.javaagent.tooling.Utils;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import java.lang.instrument.Instrumentation;
 import java.util.logging.Logger;
 import net.bytebuddy.agent.builder.AgentBuilder;
 
 @AutoService(AgentExtension.class)
 public class InstrumentationLoader implements AgentExtension {
   private static final Logger logger = Logger.getLogger(InstrumentationLoader.class.getName());
 
-  private final InstrumentationModuleInstaller instrumentationModuleInstaller =
-      new InstrumentationModuleInstaller(
-          requireNonNull(
-              InstrumentationHolder.getInstrumentation(), "Instrumentation must not be null"));
-
   @Override
   public AgentBuilder extend(AgentBuilder agentBuilder, ConfigProperties config) {
+    Instrumentation instrumentation =
+        requireNonNull(
+            InstrumentationHolder.getInstrumentation(), "Instrumentation must not be null");
+    InstrumentationModuleInstaller instrumentationModuleInstaller =
+        new InstrumentationModuleInstaller(instrumentation);
     int numberOfLoadedModules = 0;
     ClassLoader extensionsClassLoader =
         requireNonNull(