openolat#214: NPE when copying structure node with expert rule

src/main/java/de/bps/course/nodewizard/coursenode/AbstractCourseNodeCopyConfigurator.java

@@ -145,13 +145,14 @@ public class AbstractCourseNodeCopyConfigurator implements ICourseNodeCopyConfig
 	}
 
 	protected String replaceIdsInCondition(String condition) {
+		if (condition != null) {
+			condition = KeyAndNameConverter.convertExpressionKeyToKey(condition, courseEnvMapper);
 
-		condition = KeyAndNameConverter.convertExpressionKeyToKey(condition, courseEnvMapper);
-
-		for (String nodeSourceId : courseEnvMapper.getNodeSourceIds()) {
-			condition = condition.replaceAll(
-					"\"" + nodeSourceId + "\"",
-					"\"" + courseEnvMapper.getNodeTargetIdent(nodeSourceId) + "\"");
+			for (String nodeSourceId : courseEnvMapper.getNodeSourceIds()) {
+				condition = condition.replaceAll(
+						"\"" + nodeSourceId + "\"",
+						"\"" + courseEnvMapper.getNodeTargetIdent(nodeSourceId) + "\"");
+			}
 		}
 		return condition;
 	}