fix case when list of items is empty

src/main/java/com/soebes/maven/plugins/iterator/AbstractIteratorMojo.java

@@ -335,11 +335,15 @@ public void setFolder( File folder )
         this.folder = folder;
     }
 
+    protected boolean atLeastOneItemFound()throws MojoExecutionException
+    {
+        return (getItemsConverted().size()>0);
+    }
     protected boolean isMoreThanOneSet()
     {
         // a ^ b ^ c && ! (a && b && c)
         boolean result = isItemsSet() ^ isContentSet() ^ isItemsWithPropertiesSet() ^ isFolderSet()
-            && !( isItemsSet() && isContentSet() && isItemsWithPropertiesSet() && isFolderSet() );
+                && !( isItemsSet() && isContentSet() && isItemsWithPropertiesSet() && isFolderSet() );
         return !result;
     }
 

src/main/java/com/soebes/maven/plugins/iterator/IteratorMojo.java

@@ -218,11 +218,15 @@ public void execute()
             throw new MojoExecutionException( "You have to use at least one. " + "Either items element, "
                 + "itemsWithProperties, content or folder element!" );
         }
-
-        if ( isMoreThanOneSet() )
+        if(atLeastOneItemFound())
         {
-            throw new MojoExecutionException( "You can use only one element. "
-                + "Either items, itemsWithProperties, content or folder element but not more than one of them." );
+            if ( isMoreThanOneSet() )
+            {
+                throw new MojoExecutionException( "You can use only one element. "
+                    + "Either items, itemsWithProperties, content or folder element but not more than one of them." );
+            }
+        }else{
+            getLog().info( "The list of items to iterate on is empty. Nothing will be done..." );
         }
 
         List<Exception> exceptions = new ArrayList<>();