diff --git a/src/main/java/JavaFXLibrary.java b/src/main/java/JavaFXLibrary.java
index 8e9dd06..f56137c 100644
--- a/src/main/java/JavaFXLibrary.java
+++ b/src/main/java/JavaFXLibrary.java
@@ -124,7 +124,6 @@ public Object runKeyword(String keywordName, List args, Map kwargs) {
                     // timeout already expired, catch exception and jump out
                     retExcep.set(jfxte);
                     throw jfxte;
-
                 } catch (RuntimeException e) {
                     // catch exception and continue trying
                     retExcep.set(e);
@@ -142,6 +141,11 @@ public Object runKeyword(String keywordName, List args, Map kwargs) {
             } else if (e.getCause() instanceof JavaFXLibraryNonFatalException) {
                 RobotLog.trace("JavaFXLibrary: Caught JavaFXLibrary NON-FATAL exception: \n" + Throwables.getStackTraceAsString(e));
                 throw e;
+            } else if (e.getCause() instanceof IllegalArgumentException) {
+                RobotLog.trace("JavaFXLibrary: Caught IllegalArgumentException: \n" + Throwables.getStackTraceAsString(e));
+                throw new JavaFXLibraryNonFatalException("Illegal arguments for keyword '" + keywordName + "':\n" +
+                        "    ARGS: " + Arrays.toString(args.toArray()) + "\n" +
+                        "    KWARGS: " + Arrays.toString(kwargs.entrySet().toArray()));
             } else {
                 RobotLog.trace("JavaFXLibrary: Caught JavaFXLibrary RUNTIME exception: \n" + Throwables.getStackTraceAsString(e));
                 throw e;
diff --git a/src/main/java/javafxlibrary/utils/HelperFunctions.java b/src/main/java/javafxlibrary/utils/HelperFunctions.java
index b932560..506c7ed 100644
--- a/src/main/java/javafxlibrary/utils/HelperFunctions.java
+++ b/src/main/java/javafxlibrary/utils/HelperFunctions.java
@@ -902,7 +902,7 @@ public static Object[] useMappedObjects(Object[] arr) {
                 if (objectMap.containsKey(o)) {
                     replaced[i] = objectMap.get(o);
                 } else {
-                    replaced[i] = arr[i];
+                    replaced[i] = checkForNullArgument(arr[i]);
                 }
             }
         }
@@ -924,7 +924,7 @@ public static List<Object> useMappedObjects(List<Object> list) {
                 if (objectMap.containsKey(o)) {
                     replaced.set(i, objectMap.get(o));
                 } else {
-                    replaced.set(i, o);
+                    replaced.set(i, checkForNullArgument(o));
                 }
             }
         }
@@ -944,13 +944,21 @@ public static Map<String, Object> useMappedObjects(Map<String, Object> map) {
                 if (objectMap.containsKey(o)) {
                     replaced.put(key, objectMap.get(o));
                 } else {
-                    replaced.put(key, o);
+                    replaced.put(key, checkForNullArgument(o));
                 }
             }
         }
         return replaced;
     }
 
+    public static Object checkForNullArgument(Object o) {
+        if (o.getClass() == String.class && o.equals("")) {
+            return null;
+        }
+        return o;
+    }
+
+
     public static Object[] checkMethodArguments(Object[] arguments) {
         Object[] replaced = new Object[arguments.length];
         for (int i = 0; i < arguments.length; i++) {
diff --git a/src/test/robotframework/acceptance/FindTest.robot b/src/test/robotframework/acceptance/FindTest.robot
index 10aa0ac..d954d68 100644
--- a/src/test/robotframework/acceptance/FindTest.robot
+++ b/src/test/robotframework/acceptance/FindTest.robot
@@ -207,6 +207,18 @@ Previous Query Returns Nothing In Chained Selector With Find All When failIfNotF
     ${msg}                      Run Keyword And Expect Error    *    Find All    css=VBox css=ZBox Pane id=lime    true
     Should Be Equal             Find operation failed for query: "css=VBox css=ZBox Pane id=lime"    ${msg}
 
+Find With Nonvalid Root
+    [Tags]                      smoke    negative
+    Set Test Application        ${BOUNDS_APP}
+    ${msg}                      Run Keyword And Expect Error    *    Find            xpath=//Rectangle[@width="75.0"]    false    not-a-valid-root
+    Should Start With           ${msg}                          Illegal arguments for keyword 'find'
+
+Find All With Nonvalid Root
+    [Tags]                      smoke    negative
+    Set Test Application        ${BOUNDS_APP}
+    ${msg}                      Run Keyword And Expect Error    *    Find All        xpath=//Rectangle[@width="75.0"]    false    not-a-valid-root
+    Should Start With           ${msg}                          Illegal arguments for keyword 'findAll'
+
 Find Labeled Node With Text
     [Tags]                      smoke
     Set Test Application        javafxlibrary.testapps.TestWindowManagement