revert nullchecks on base decorator

Author: amarziali

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/decorator/BaseDecorator.java

@@ -78,9 +78,7 @@ public AgentSpan afterStart(final AgentSpan span) {
   }
 
   public ContextScope beforeFinish(final ContextScope scope) {
-    if (scope != null) {
-      beforeFinish(scope.context());
-    }
+    beforeFinish(scope.context());
     return scope;
   }