What causes "The function call writeToLog requires 1 or 2 arguments." in pentaho/pentaho-kettle?

Call with 1 or 2 arguments: writeToLog('message') or writeToLog('logRowlevel', 'message').

The function call writeToLog requires 1 or 2 arguments.

Error message

The function call writeToLog requires 1 or 2 arguments.

What it means

writeToLog writes a message to the transformation log, optionally with a log level as the first argument, so it accepts exactly 1 or 2 arguments; any other argument count (including zero, or three) hits the default branch of its switch and throws this error.

Solutions

Call with 1 or 2 arguments: writeToLog('message') or writeToLog('logRowlevel', 'message').
Use a valid log level constant string ('Basic','Detailed','Error','Debug','Rowlevel') as first argument when using two.
Remove extra parameters; concatenate them into the message instead.

Example fix

// before
writeToLog('Debug', 'value=', val, 'id=', id);
// after
writeToLog('Debug', 'value=' + val + ' id=' + id);

Defensive patterns

Strategy: validation

Validate before calling

function safeLog(level, msg) {
  if (arguments.length < 1) return;
  if (arguments.length === 1) writeToLog(String(arguments[0]));
  else writeToLog(String(level), String(msg));
}
safeLog('Debug', 'value=' + val);

Prevention

Always pass 1 (message) or 2 (level, message) arguments, never more.
Concatenate multiple values into a single message string.
Use standard level strings: Basic, Detailed, Error, Debug, Rowlevel.

When it happens

Trigger: writeToLog() with no arguments, or writeToLog(a, b, c) with three arguments, in a Modified Java Script Value step.

Common situations: Adding a message parameter to an existing 2-arg call (level, message) producing 3 args; calling it to test without arguments; passing the level and message in the wrong slots then appending extras.

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

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/713384a49388804f. Report an issue: GitHub.

Appendix: source

Thrown at engine/src/main/java/org/pentaho/di/trans/steps/scriptvalues_mod/ScriptValuesAddedFunctions.java:338

              scm.logBasic( strMessage );
            } else if ( strType.equals( "d" ) ) {
              scm.logDebug( strMessage );
            } else if ( strType.equals( "l" ) ) {
              scm.logDetailed( strMessage );
            } else if ( strType.equals( "e" ) ) {
              scm.logError( strMessage );
            } else if ( strType.equals( "m" ) ) {
              scm.logMinimal( strMessage );
            } else if ( strType.equals( "r" ) ) {
              scm.logRowlevel( strMessage );
            }
          }
        } catch ( Exception e ) {
          // Ignore errors
        }
        break;
      default:
        throw Context.reportRuntimeError( "The function call writeToLog requires 1 or 2 arguments." );
    }
  }

  private static boolean isUndefined( Object ArgList ) {
    return isUndefined( new Object[] { ArgList }, new int[] { 0 } );
  }

  private static boolean isUndefined( Object[] ArgList, int[] iArrToCheck ) {
    for ( int i = 0; i < iArrToCheck.length; i++ ) {
      if ( ArgList[iArrToCheck[i]].equals( Context.getUndefinedValue() ) ) {
        return true;
      }
    }
    return false;
  }

  private static boolean isNull( Object ArgList ) {
    return isNull( new Object[] { ArgList }, new int[] { 0 } );

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