diff --git a/docs-core/src/main/java/com/sismics/util/mime/MimeTypeUtil.java b/docs-core/src/main/java/com/sismics/util/mime/MimeTypeUtil.java
index 427ae387..0a9ea3d7 100644
--- a/docs-core/src/main/java/com/sismics/util/mime/MimeTypeUtil.java
+++ b/docs-core/src/main/java/com/sismics/util/mime/MimeTypeUtil.java
@@ -27,7 +27,8 @@ public class MimeTypeUtil {
      * @throws IOException e
      */
     public static String guessMimeType(Path file, String name) throws IOException {
-        String mimeType = URLConnection.getFileNameMap().getContentTypeFor(name);
+        String mimeType = name == null ?
+                null : URLConnection.getFileNameMap().getContentTypeFor(name);
         if (mimeType == null) {
             try (InputStream is = Files.newInputStream(file)) {
                 final byte[] headerBytes = new byte[64];
diff --git a/docs-core/src/test/java/com/sismics/util/TestMimeTypeUtil.java b/docs-core/src/test/java/com/sismics/util/TestMimeTypeUtil.java
index b6e64299..1fa18fb1 100644
--- a/docs-core/src/test/java/com/sismics/util/TestMimeTypeUtil.java
+++ b/docs-core/src/test/java/com/sismics/util/TestMimeTypeUtil.java
@@ -27,5 +27,8 @@ public class TestMimeTypeUtil {
         // Detect PPTX files
         path = Paths.get(ClassLoader.getSystemResource("file/apache.pptx").toURI());
         Assert.assertEquals(MimeType.OFFICE_PRESENTATION, MimeTypeUtil.guessMimeType(path, "apache.pptx"));
+
+        // Detect TXT files
+        Assert.assertEquals(MimeType.TEXT_PLAIN, MimeTypeUtil.guessMimeType(path, "file.txt"));
     }
 }