Use null for effective log home when not set

Author: rjeberhard

operator/src/main/java/oracle/kubernetes/operator/helpers/JobStepContext.java

@@ -99,7 +99,7 @@ protected boolean isDomainHomeInImage() {
   }
 
   String getEffectiveLogHome() {
-    if (!getDomain().getLogHomeEnabled()) return "";
+    if (!getDomain().getLogHomeEnabled()) return null;
     String logHome = getLogHome();
     if (logHome == null || "".equals(logHome.trim())) {
       // logHome not specified, use default value

operator/src/main/java/oracle/kubernetes/operator/helpers/PodStepContext.java

@@ -143,7 +143,7 @@ protected boolean isDomainHomeInImage() {
   }
 
   String getEffectiveLogHome() {
-    if (!getDomain().getLogHomeEnabled()) return "";
+    if (!getDomain().getLogHomeEnabled()) return null;
     String logHome = getLogHome();
     if (logHome == null || "".equals(logHome.trim())) {
       // logHome not specified, use default value

operator/src/test/java/oracle/kubernetes/operator/helpers/PodHelperTestBase.java

@@ -326,7 +326,7 @@ public void whenPodCreated_hasPredefinedEnvVariables() {
             hasEnvVar("DOMAIN_UID", UID),
             hasEnvVar("NODEMGR_HOME", NODEMGR_HOME),
             hasEnvVar("SERVER_OUT_IN_POD_LOG", Boolean.toString(INCLUDE_SERVER_OUT_IN_POD_LOG)),
-            hasEnvVar("LOG_HOME", ""),
+            hasEnvVar("LOG_HOME", null),
             hasEnvVar("SERVICE_NAME", LegalNames.toServerServiceName(UID, getServerName())),
             hasEnvVar("AS_SERVICE_NAME", LegalNames.toServerServiceName(UID, ADMIN_SERVER))));
   }
@@ -622,7 +622,7 @@ V1Container createPodSpecContainer() {
         .addEnvItem(envItem("NODEMGR_HOME", NODEMGR_HOME))
         .addEnvItem(
             envItem("SERVER_OUT_IN_POD_LOG", Boolean.toString(INCLUDE_SERVER_OUT_IN_POD_LOG)))
-        .addEnvItem(envItem("LOG_HOME", ""))
+        .addEnvItem(envItem("LOG_HOME", null))
         .addEnvItem(envItem("SERVICE_NAME", LegalNames.toServerServiceName(UID, getServerName())))
         .addEnvItem(envItem("AS_SERVICE_NAME", LegalNames.toServerServiceName(UID, ADMIN_SERVER)))
         .livenessProbe(createLivenessProbe())