fix: do not throw exception in case of empty url

In case of an empty `url` parameter, the SDK should not crash the application. The logging SDK is likely not as critical to the consumer business flow to the degree, that providing an incorrect argument would kill the whole process.

parsely/src/main/java/com/parsely/parselyandroid/ParselyTracker.java

@@ -222,7 +222,8 @@ public void trackPageview(
             @Nullable ParselyMetadata urlMetadata,
             @Nullable Map<String, Object> extraData) {
         if (url.equals("")) {
-            throw new IllegalArgumentException("url cannot be null or empty.");
+            log("url cannot be empty");
+            return;
         }
 
         // Blank urlref is better than null
@@ -262,7 +263,8 @@ public void startEngagement(
             final @Nullable Map<String, Object> extraData
     ) {
         if (url.equals("")) {
-            throw new IllegalArgumentException("url cannot be null or empty.");
+            log("url cannot be empty");
+            return;
         }
 
         // Blank urlref is better than null
@@ -320,7 +322,8 @@ public void trackPlay(
             @NonNull ParselyVideoMetadata videoMetadata,
             @Nullable Map<String, Object> extraData) {
         if (url.equals("")) {
-            throw new IllegalArgumentException("url cannot be null or empty.");
+            log("url cannot be empty");
+            return;
         }
 
         // Blank urlref is better than null