add Initializer annotation

Author: zeitlinger

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/internal/Initializer.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.api.internal;
+
+/**
+ * See <a href="https://github.com/uber/NullAway/wiki/Supported-Annotations#initialization">NullAway
+ * spec</a>
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public @interface Initializer {}

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/internal/InstrumenterUtil.java

@@ -19,16 +19,17 @@
  * This class is internal and is hence not for public use. Its APIs are unstable and can change at
  * any time.
  */
-@SuppressWarnings("NullAway") // setters called in static initializer
 public final class InstrumenterUtil {
 
   private static InstrumenterAccess instrumenterAccess;
   private static InstrumenterBuilderAccess instrumenterBuilderAccess;
 
+  @Initializer
   public static void setInstrumenterAccess(InstrumenterAccess instrumenterAccess) {
     InstrumenterUtil.instrumenterAccess = instrumenterAccess;
   }
 
+  @Initializer
   public static void setInstrumenterBuilderAccess(
       InstrumenterBuilderAccess instrumenterBuilderAccess) {
     InstrumenterUtil.instrumenterBuilderAccess = instrumenterBuilderAccess;