if (getFieldInfo(name) != null) {
if (fieldInfo.get(name) != null) {
    public void declare_field(int modifiers, Class type, String name) {        if (getFieldInfo(name) != null) {            throw new IllegalArgumentException("Field \"" + name + "\" already exists");        }        backend.declare_field(modifiers, type, name);        fieldInfo.put(name, new FieldInfo(Modifier.isStatic(modifiers), type));    }