KEYCLOAK-12281 Fix export/import for users that have custom credential algorithms with no salt

- do not swallow exception when decoding salt

server-spi/src/main/java/org/keycloak/models/credential/dto/PasswordSecretData.java

@@ -16,7 +16,7 @@ public class PasswordSecretData {
 
     @JsonCreator
     public PasswordSecretData(@JsonProperty("value") String value, @JsonProperty("salt") String salt) throws IOException {
-        if ("__SALT__".equals(salt)) {
+        if (salt == null || "__SALT__".equals(salt)) {
             this.value = value;
             this.salt = null;
         }