Bugfix in preproc due to PTA syntax checks.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@1925 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/parser/visitor/SemanticCheck.java

@@ -360,7 +360,7 @@ public class SemanticCheck extends ASTTraverse
 	public void visitPost(ExpressionVar e) throws PrismLangException
 	{
 		// For PTAs, references to variables in modules have to be local
-		if (modulesFile.getModelType() == ModelType.PTA && module != null) {
+		if (modulesFile != null && modulesFile.getModelType() == ModelType.PTA && module != null) {
 			if (!module.isLocalVariable(e.getName())) {
 				throw new PrismLangException("Modules in a PTA cannot access non-local variables", e);
 			}