9355 - Fix NullPointerException log in AppSec (#9356)

Backport #9355 to release/v1.52.x

Author: jandro996

dd-java-agent/appsec/src/main/java/com/datadog/appsec/ddwaf/WAFModule.java

@@ -1,5 +1,6 @@
 package com.datadog.appsec.ddwaf;
 
+import static datadog.trace.api.telemetry.LogCollector.SEND_TELEMETRY;
 import static datadog.trace.util.stacktrace.StackTraceEvent.DEFAULT_LANGUAGE;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
@@ -557,6 +558,10 @@ private Waf.ResultWithData runWafTransient(
   }
 
   private Collection<AppSecEvent> buildEvents(Waf.ResultWithData actionWithData) {
+    if (actionWithData.data == null) {
+      log.debug(SEND_TELEMETRY, "WAF result data is null");
+      return Collections.emptyList();
+    }
     Collection<WAFResultData> listResults;
     try {
       listResults = RES_JSON_ADAPTER.fromJson(actionWithData.data);

dd-java-agent/appsec/src/test/groovy/com/datadog/appsec/ddwaf/WAFModuleSpecification.groovy

@@ -1682,6 +1682,19 @@ class WAFModuleSpecification extends DDSpecification {
     internal == libddwaf
   }
 
+  void 'ResultWithData - null data'() {
+    def waf = new WAFModule()
+    Waf.ResultWithData rwd = new Waf.ResultWithData(null, null, null, null)
+    Collection ret
+
+    when:
+    ret = waf.buildEvents(rwd)
+
+    then:
+    noExceptionThrown()
+    ret.isEmpty()
+  }
+
   /**
    * Helper to return a concrete Waf exception for each WafErrorCode
    */