diff --git a/src/OpCrypto.java b/src/OpCrypto.java
index cd91626..13cb231 100644
--- a/src/OpCrypto.java
+++ b/src/OpCrypto.java
@@ -65,7 +65,7 @@ public byte[] hashFd(StreamDeserializationContext ctx) {
         try {
             MessageDigest digest = MessageDigest.getInstance(this._HASHLIB_NAME());
             byte[] chunk = ctx.read(1048576);
-            while (chunk.length>0){
+            while (chunk!=null && chunk.length>0){
                 digest.update(chunk);
                 chunk = ctx.read(1048576);
             }
diff --git a/src/OpenTimestamps.java b/src/OpenTimestamps.java
index 0336e5e..80d97e9 100644
--- a/src/OpenTimestamps.java
+++ b/src/OpenTimestamps.java
@@ -130,7 +130,7 @@ public static String verify(byte[]ots, byte[]plain, Boolean isHash) {
             StreamDeserializationContext ctx = new StreamDeserializationContext(ots);
             detachedTimestamp = DetachedTimestampFile.deserialize(ctx);
         } catch (Exception e) {
-
+            System.err.print("StreamDeserializationContext error");
         }
 
         byte[] actualFileDigest = new byte[0];
@@ -140,14 +140,14 @@ public static String verify(byte[]ots, byte[]plain, Boolean isHash) {
                 StreamDeserializationContext ctxHashfd = new StreamDeserializationContext(plain);
                 actualFileDigest = ((OpCrypto)(detachedTimestamp.fileHashOp)).hashFd(ctxHashfd);
             } catch (Exception e) {
-
+                System.err.print("StreamDeserializationContext : file stream error");
             }
         } else {
             // Read Hash
             try {
                 actualFileDigest = plain.clone();
             } catch (Exception e) {
-
+                System.err.print("StreamDeserializationContext : file hash error");
             }
         }