Object[] previousRow;
RowMetaInterface outputMeta;

public boolean processRow(StepMetaInterface smi, StepDataInterface sdi) throws KettleException
{
    // First, get a row from the default input hop
    Object[] r = getRow();

    // If the row object is null, we are done processing.
    if (r == null) {
      setOutputDone();
      return false;
    }

	if (outputMeta == null) {
	    outputMeta = data.outputRowMeta.clone();
        for(int i=0; i < outputMeta.size(); i++) {
			ValueMetaInterface meta = outputMeta.getValueMeta(i);
		    if (meta.getType() == ValueMetaInterface.TYPE_NUMBER) {
				meta.setPrecision(4);
				meta.setConversionMask("#.####");
			}
        }    
    }

    // It is always safest to call createOutputRow() to ensure that your output row's Object[] is large
    // enough to handle any new fields you are creating in this step.
    Object[] outputRow = createOutputRow(r, data.outputRowMeta.size());

    // copy all input fields to the output fields

    for (int i=0; i < getInputRowMeta().size(); i++) {
        if ((r[i] == null) && (previousRow != null))  {
            // if the current field is empty take it from the previous row
            outputRow[i] = previousRow[i];
        }   
        else {
            // otherwise use the current row
            outputRow[i] = r[i];
        }

    }

    putRow(outputMeta, outputRow);
    // store the current row as future previous row
    previousRow = outputMeta.cloneRow(outputRow);

    return true;
}