apache/druid · error · IAE

Cannot create type [ ]

Error message

Cannot create type [%s]

What it means

ExprEval.ofType converts a deserialized value into an ExprEval of the requested type. For a null-typed or otherwise unhandled ExpressionType it falls through the switch and throws IAE 'Cannot create type'. Arrays and non-array mismatches are handled by bestEffortOf+castTo, so this only fires for types entirely outside the supported set.

Solutions

1. Use a supported ExpressionType (LONG, LONG_ARRAY, DOUBLE, DOUBLE_ARRAY, STRING, STRING_ARRAY, COMPLEX, etc.) when calling ofType
2. If the input value may mismatch, call ExprEval.bestEffortOf(value).castTo(type) yourself instead of ofType
3. Check the serialized type signature producing the value; fix the writer side

Example fix

// before
ExprEval.ofType(ExpressionType.fromTypeFull(NullType.NAME), value);
// after
ExprEval.bestEffortOf(value).castTo(ExpressionType.STRING);

switch (type.getFactory()) {
  case LONG: case LONG_ARRAY: case DOUBLE: case DOUBLE_ARRAY:
  case STRING: case STRING_ARRAY: case COMPLEX: /* ok */ break;
  default: throw new IllegalArgumentException("unsupported type " + type);
}

try {
  eval = ExprEval.ofType(type, value);
} catch (IllegalArgumentException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Cannot create type")) {
    eval = ExprEval.bestEffortOf(value).castTo(ExpressionType.STRING);
  } else { throw e; }
}

When it happens

Trigger: Calling ExprEval.ofType(type, value) with an ExpressionType whose registry kind is not handled (e.g. a null-typed type or a newly added type not yet supported).

Common situations: Deserializing values with a corrupted or unexpected type signature; custom code constructing ExpressionType instances outside the standard registry; version skew where a newer type is read by older code.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Cannot add / to a Spectator Histogram
• Cannot cast [ ] to [ ] (Types.InvalidCastException from…
• Cannot deserialize type
• Cannot implicitly cast
• needs a LONG as its second argument but got

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/a47efb215807ca76. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/math/expr/ExprEval.java:621

          }
          return ofArray(type, array);
        }

        if (value instanceof Object[]) {
          Object[] inputArray = (Object[]) value;
          Object[] array = new Object[inputArray.length];
          int i = 0;
          for (Object o : inputArray) {
            array[i++] = ExprEval.ofType(elementType, o).value();
          }
          return ofArray(type, array);
        }
        // in a better world, we might get an object that matches the type signature for arrays and could do a switch
        // statement here, but this is not that world yet, and things that are array typed might also be non-arrays,
        // e.g. we might get a String instead of String[], so just fallback to bestEffortOf
        return bestEffortOf(value).castTo(type);
    }
    throw new IAE("Cannot create type [%s]", type);
  }

  @Nullable
  public static Number computeNumber(@Nullable String value)
  {
    if (value == null) {
      return null;
    }
    if (Evals.asBoolean(value)) {
      return 1.0;
    }
    if (value.equalsIgnoreCase("false")) {
      return 0.0;
    }
    Number rv;
    Long v = GuavaUtils.tryParseLong(value);
    // Do NOT use ternary operator here, because it makes Java to convert Long to Double
    if (v != null) {

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