diff --git a/core/src/main/java/org/bitcoinj/wallet/DeterministicSeed.java b/core/src/main/java/org/bitcoinj/wallet/DeterministicSeed.java
index 38a7ac84a..3743c7f48 100644
--- a/core/src/main/java/org/bitcoinj/wallet/DeterministicSeed.java
+++ b/core/src/main/java/org/bitcoinj/wallet/DeterministicSeed.java
@@ -52,8 +52,8 @@ public class DeterministicSeed implements EncryptableItem {
     @Nullable private final EncryptedData encryptedSeed;
     private long creationTimeSeconds;
 
-    public DeterministicSeed(String mnemonicCode, byte[] seed, String passphrase, long creationTimeSeconds) throws UnreadableWalletException {
-        this(decodeMnemonicCode(mnemonicCode), seed, passphrase, creationTimeSeconds);
+    public DeterministicSeed(String mnemonicString, byte[] seed, String passphrase, long creationTimeSeconds) throws UnreadableWalletException {
+        this(decodeMnemonicCode(mnemonicString), seed, passphrase, creationTimeSeconds);
     }
 
     public DeterministicSeed(byte[] seed, List<String> mnemonic, long creationTimeSeconds) {
@@ -139,11 +139,11 @@ public class DeterministicSeed implements EncryptableItem {
     }
 
     public String toString(boolean includePrivate) {
-        MoreObjects.ToStringHelper helper = MoreObjects.toStringHelper(this);
+        MoreObjects.ToStringHelper helper = MoreObjects.toStringHelper(this).omitNullValues();
         if (isEncrypted())
             helper.addValue("encrypted");
         else if (includePrivate)
-            helper.addValue(toHexString()).add("mnemonicCode", Utils.SPACE_JOINER.join(mnemonicCode));
+            helper.addValue(toHexString()).add("mnemonicCode", getMnemonicString());
         else
             helper.addValue("unencrypted");
         return helper.toString();
@@ -200,7 +200,7 @@ public class DeterministicSeed implements EncryptableItem {
     }
 
     private byte[] getMnemonicAsBytes() {
-        return Utils.SPACE_JOINER.join(mnemonicCode).getBytes(StandardCharsets.UTF_8);
+        return getMnemonicString().getBytes(StandardCharsets.UTF_8);
     }
 
     public DeterministicSeed decrypt(KeyCrypter crypter, String passphrase, KeyParameter aesKey) {
@@ -247,6 +247,12 @@ public class DeterministicSeed implements EncryptableItem {
         return mnemonicCode;
     }
 
+    /** Get the mnemonic code as string, or null if unknown. */
+    @Nullable
+    public String getMnemonicString() {
+        return mnemonicCode != null ? Utils.SPACE_JOINER.join(mnemonicCode) : null;
+    }
+
     private static List<String> decodeMnemonicCode(byte[] mnemonicCode) {
         return decodeMnemonicCode(new String(mnemonicCode, StandardCharsets.UTF_8));
     }