de.congrace.exp4j fails on multiple arguments for a CustomFunction
<p>i am trying to add a custom function that sums number to a ExpressionBuilder
This is the java code:</p>

<pre><code>package com.sapiens.bdms.drools.exe.helper.FuncServiceTrial;

import com.sapiens.bdms.drools.exe.helper.Functions;
import de.congrace.exp4j.*;

import java.util.ArrayList;
import java.util.Collection;


public class FormulaInterpreter {

    public double interpret(String formula) throws UnparsableExpressionException, UnknownFunctionException, InvalidCustomFunctionException {
        Collection&lt;CustomFunction&gt; customFunctions = new ArrayList&lt;CustomFunction&gt;();
        customFunctions.add(new CustomFunction("SUM") {
            @Override
            public double applyFunction(double[] doubles) {
                Double res = 0.0;
                for (double aDouble : doubles) {
                    res += aDouble;
                }
                return res;
            }
        });
        Calculable calc = (Calculable) new ExpressionBuilder(formula).withCustomFunctions(customFunctions).build();
        return calc.calculate();
    }

    public static void main(String[] args) throws UnknownFunctionException, UnparsableExpressionException, InvalidCustomFunctionException {
        FormulaInterpreter formulaInterpreter = new FormulaInterpreter();
        double res = formulaInterpreter.interpret("SUM(2,4,4)");
        System.out.println(res);
    }
}
</code></pre>

<p>but it prints out "2" instad of 10</p>
