pentaho/pentaho-kettle · error · IllegalArgumentException

Key already added [key= ]

Error message

Key already added [key={key}]

What it means

KeyValueSet.add() enforces unique keys within the set. If a KeyValue with an already-present key is added, it throws IllegalArgumentException('Key already added [key=...]'). KeyValueSet is a keyed collection, so duplicate keys would silently overwrite otherwise.

Solutions

1. Deduplicate the KeyValue array before calling add (e.g. via a LinkedHashMap keyed by getKey()).
2. Decide on overwrite semantics: remove the existing entry first or use put()/update if the API supports replacing.
3. Log or surface the duplicate source item instead of adding it blindly.

Example fix

// before
set.add(new KeyValue<>("retries", 3));
set.add(new KeyValue<>("retries", 5)); // throws
// after
Map<String, KeyValue<?>> unique = new LinkedHashMap<>();
for (KeyValue<?> kv : keyValues) unique.putIfAbsent(kv.getKey(), kv);
set.add(unique.values().toArray(new KeyValue<?>[0]));

Set<String> seen = new HashSet<>();
for (KeyValue<?> kv : keyValues) {
  if (!seen.add(kv.getKey())) {
    throw new IllegalArgumentException("Duplicate key in input: " + kv.getKey());
  }
}

try {
  set.add(keyValues);
} catch (IllegalArgumentException e) {
  // extract duplicate key from message and report source item, or deduplicate and retry
}

When it happens

Trigger: Calling add(keyValue...) (or the fluent chain) with two KeyValue instances sharing the same key, including re-adding a key that was added in a previous add() call on the same set.

Common situations: Building a set from a list of parsed parameters where duplicates exist (repeated query/CLI parameters); loop code re-adding the same KeyValue; copy-paste of field definitions.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Destination must be a folder / invalid drag-drop source…
• is already included.
• Key contains invalid characters
• Key must not be '_'
• Key must not end with '-'

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/626510b44848f489. Report an issue: GitHub.

Appendix: source

Thrown at engine/src/main/java/org/pentaho/di/core/util/KeyValueSet.java:54

  /**
   * Serial version UID.
   */
  private static final long serialVersionUID = 925133158112717153L;

  private final Map<String, KeyValue<?>> entries = new TreeMap<String, KeyValue<?>>();

  /**
   * Add key value(s).
   *
   * @param keyValues
   *          key values to add.
   * @return this.
   */
  public KeyValueSet add( final KeyValue<?>... keyValues ) {
    for ( KeyValue<?> keyValue : keyValues ) {
      if ( this.entries.containsKey( keyValue.getKey() ) ) {
        throw new IllegalArgumentException( "Key already added [key=" + keyValue.getKey() + "]" );
      }
      this.entries.put( keyValue.getKey(), keyValue );
    }
    return this;
  }

  /**
   * {@inheritDoc}
   *
   * @see java.lang.Iterable#iterator()
   */
  public Iterator<KeyValue<?>> iterator() {
    return this.keyValues().iterator();
  }

  /**
   * @param key
   *          the key.

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