pentaho/pentaho-kettle · error · RuntimeException

The function call month requires 1 argument.

Error message

The function call month requires 1 argument.

What it means

Arity guard in ScriptAddedFunctions.month: the script call's ArgList length is not 1. The single expected argument is a java.util.Date; with correct arity the function returns the Calendar month as a Double, otherwise this RuntimeException is thrown to the script engine.

Solutions

1. Call month() with exactly one Date argument.
2. Remember the result is 0-based; add 1 for human-readable months.
3. Convert strings with str2date() first.
4. Null-check the date before the call.

Example fix

// before
var m = month();
// after
var m = month(dateField) + 1; // Calendar.MONTH is 0-based

var m = (d != null) ? month(d) + 1 : null; // Calendar.MONTH is 0-based

function isKettleDate(v) { return v != null && v instanceof java.util.Date; }

try {
  var m = month(d);
} catch (e) {
  Logger.LogBasic("month failed: " + e.message);
  m = null;
}

When it happens

Trigger: Calling month() with zero or multiple arguments in a Script step, or an argument flow that fails the ArgList.length == 1 check.

Common situations: Expecting 1-based months (Calendar.MONTH is 0-based, January = 0); passing string dates; chaining calls with wrong arity.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• The function call quarter requires 1 argument.
• The function call week requires 1 argument.
• The function call year requires 1 argument.
• The function call lpad requires 3 arguments.
• The function call rpad requires 3 arguments.

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/6643d9125dde2cd7. Report an issue: GitHub.

Appendix: source

Thrown at engine/src/main/java/org/pentaho/di/trans/steps/script/ScriptAddedFunctions.java:862

      throw new RuntimeException( e.toString() );
    }
  }

  public static Object month( ScriptEngine actualContext, Bindings actualObject, Object[] ArgList,
    Object FunctionContext ) {
    try {
      if ( ArgList.length == 1 ) {
        if ( isNull( ArgList[0] ) ) {
          return new Double( Double.NaN );
        } else if ( isUndefined( ArgList[0] ) ) {
          return undefinedValue;
        }
        java.util.Date dArg1 = (java.util.Date) ArgList[0];
        Calendar cal = Calendar.getInstance();
        cal.setTime( dArg1 );
        return new Double( cal.get( Calendar.MONTH ) );
      } else {
        throw new RuntimeException( "The function call month requires 1 argument." );
      }
    } catch ( Exception e ) {
      throw new RuntimeException( e.toString() );
    }

  }

  public static Object quarter( ScriptEngine actualContext, Bindings actualObject, Object[] ArgList,
    Object FunctionContext ) {
    try {
      if ( ArgList.length == 1 ) {
        if ( isNull( ArgList[0] ) ) {
          return new Double( Double.NaN );
        } else if ( isUndefined( ArgList[0] ) ) {
          return undefinedValue;
        }
        java.util.Date dArg1 = (java.util.Date) ArgList[0];
        Calendar cal = Calendar.getInstance();

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