CAY-2785 Modeler: improve folder selection for cgen
 - refactor output-dir related methods in cgen
diff --git a/cayenne-cgen/src/main/java/org/apache/cayenne/gen/CgenConfiguration.java b/cayenne-cgen/src/main/java/org/apache/cayenne/gen/CgenConfiguration.java
index e550f70..2b73571 100644
--- a/cayenne-cgen/src/main/java/org/apache/cayenne/gen/CgenConfiguration.java
+++ b/cayenne-cgen/src/main/java/org/apache/cayenne/gen/CgenConfiguration.java
@@ -238,10 +238,7 @@
      */
     public Path buildOutputPath() {
         if (rootProjectPath == null) {
-            if(!cgenOutputRelativePath.isAbsolute()) {
-                throw new ValidationException("Output directory is a relative path but no root is set.");
-            }
-            // this should be only in case this is a new unsaved project
+            // this could be an unsaved project or direct usage in tools (Ant, Maven or Gradle)
             return cgenOutputRelativePath;
         }