Add default implementation for getDbSystem() and fix nullable handling

Author: trask

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/db/DbClientAttributesExtractor.java

@@ -74,10 +74,11 @@ static <REQUEST, RESPONSE> void onStartCommon(
       DbClientAttributesGetter<REQUEST, RESPONSE> getter,
       REQUEST request) {
     if (SemconvStability.emitStableDatabaseSemconv()) {
+      String dbSystemName = getter.getDbSystemName(request);
       internalSet(
           attributes,
           DB_SYSTEM_NAME,
-          SemconvStability.stableDbSystemName(getter.getDbSystem(request)));
+          dbSystemName != null ? SemconvStability.stableDbSystemName(dbSystemName) : null);
       internalSet(attributes, DB_NAMESPACE, getter.getDbNamespace(request));
       internalSet(attributes, DB_QUERY_TEXT, getter.getDbQueryText(request));
       internalSet(attributes, DB_OPERATION_NAME, getter.getDbOperationName(request));

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/db/DbClientCommonAttributesGetter.java

@@ -19,7 +19,10 @@ public interface DbClientCommonAttributesGetter<REQUEST, RESPONSE> {
    * @deprecated Use {@link DbClientAttributesGetter#getDbSystemName} instead.
    */
   @Deprecated
-  String getDbSystem(REQUEST request);
+  @Nullable
+  default String getDbSystem(REQUEST request) {
+    return null;
+  }
 
   /**
    * @deprecated There is no replacement at this time.
@@ -35,7 +38,9 @@ default String getUser(REQUEST request) {
    */
   @Deprecated
   @Nullable
-  String getDbNamespace(REQUEST request);
+  default String getDbNamespace(REQUEST request) {
+    return null;
+  }
 
   /**
    * @deprecated There is no replacement at this time.

instrumentation/jdbc/library/src/main/java/io/opentelemetry/instrumentation/jdbc/internal/JdbcAttributesGetter.java

@@ -33,6 +33,7 @@ public String getUser(DbRequest request) {
     return request.getDbInfo().getUser();
   }
 
+  @SuppressWarnings("deprecation") // overriding deprecated method from parent interface
   @Nullable
   @Override
   public String getDbNamespace(DbRequest request) {