diff --git a/numass-main/src/main/java/inr/numass/NumassIO.java b/numass-main/src/main/java/inr/numass/NumassIO.java
index 068453d2..cde9755f 100644
--- a/numass-main/src/main/java/inr/numass/NumassIO.java
+++ b/numass-main/src/main/java/inr/numass/NumassIO.java
@@ -27,7 +27,9 @@ import hep.dataforge.utils.ReferenceRegistry;
 import org.apache.commons.io.output.TeeOutputStream;
 import org.slf4j.LoggerFactory;
 
-import java.io.*;
+import java.io.File;
+import java.io.IOException;
+import java.io.OutputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
@@ -105,20 +107,21 @@ public class NumassIO extends BasicIOManager {
         if (!Files.exists(parentDir)) {
             throw new RuntimeException("Working directory does not exist");
         }
-        if (dirName != null && !dirName.isEmpty()) {
-            parentDir = parentDir.resolve(dirName);
-            Files.createDirectories(parentDir);
-        }
+        try {
+            if (dirName != null && !dirName.isEmpty()) {
+                parentDir = parentDir.resolve(dirName);
+                Files.createDirectories(parentDir);
+            }
 
 //        String output = source.meta().getString("output", this.meta().getString("output", fileName + ".onComplete"));
-        outputFile = parentDir.resolve(fileName);
-        try {
+            outputFile = parentDir.resolve(fileName);
+
             if (getContext().getBoolean("numass.consoleOutput", false)) {
                 return new TeeOutputStream(Files.newOutputStream(outputFile), System.out);
             } else {
                 return Files.newOutputStream(outputFile);
             }
-        } catch (FileNotFoundException ex) {
+        } catch (IOException ex) {
             throw new RuntimeException(ex);
         }
     }
diff --git a/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java b/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
index d787ef46..c254803f 100644
--- a/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
+++ b/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
@@ -20,8 +20,7 @@ import inr.numass.models.FSS;
 import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
-import java.io.FileInputStream;
-import java.io.FileNotFoundException;
+import java.io.IOException;
 import java.io.InputStream;
 
 import static hep.dataforge.values.ValueType.BOOLEAN;
@@ -61,14 +60,19 @@ public class SterileNeutrinoSpectrum extends AbstractParametricFunction {
     public SterileNeutrinoSpectrum(Context context, Meta configuration) {
         super(list);
         if (configuration.getBoolean("useFSS", true)) {
-            InputStream fssStream;
-            if (configuration.hasValue("fssFile")) {
-                    fssStream = context.io().optBinary(configuration.getString("fssFile"))
-                            .orElseThrow(()-> new RuntimeException("Could not locate FSS file"))
-                            .getStream();
-            } else {
-                fssStream = getClass().getResourceAsStream("/data/FS.txt");
-            }
+            InputStream fssStream = configuration.optString("fssFile")
+                    .map(fssFile -> {
+                        try {
+                            return context.io().optBinary(fssFile)
+                                    .orElseThrow(() -> new RuntimeException("Could not locate FSS file"))
+                                    .getStream();
+                        } catch (IOException e) {
+                            throw new RuntimeException("Could not load FSS file", e);
+                        }
+                    })
+                    .orElse(getClass().getResourceAsStream("/data/FS.txt"));
+
+
             fss = new FSS(fssStream);
         }