Cast string error in function groupConcat about siddhi-execution-string

[tammypi]

I have already found the code which occur the error.
GroupConcatFunctionExtension.java

The code:
` @OverRide
public Object processAdd(Object o) {
addString((String) o);
return constructConcatString(",");
}

@Override
public Object processAdd(Object[] objects) {
    addString((String) objects[0]);
    return constructConcatString((String) objects[1]);
}

@Override
public Object processRemove(Object o) {
    removeString((String) o);
    return constructConcatString(",");
}

@Override
public Object processRemove(Object[] objects) {
    removeString((String) objects[0]);
    return constructConcatString((String) objects[1]);
}`

should be changed as below:

`@Override
public Object processAdd(Object o) {
addString(String.valueOf(o));
return constructConcatString(",");
}

@Override
public Object processAdd(Object[] objects) {
    addString(String.valueOf(objects[0]));
    return constructConcatString(String.valueOf(objects[1]));
}

@Override
public Object processRemove(Object o) {
    removeString(String.valueOf(o));
    return constructConcatString(",");
}

@Override
public Object processRemove(Object[] objects) {
    removeString(String.valueOf(objects[0]));
    return constructConcatString(String.valueOf(objects[1]));
}`