src/main/java/org/efaps/ui/wicket/request/EFapsRequestParametersAdapter.java
@Override
    public StringValue getParameterValue(final String _name)
    {
        final List<StringValue> values = this.parameters.get(_name);
        return (values != null && !values.isEmpty()) ? values.get(0)
                        : StringValue.valueOf((String) null);
    }
@Override
    public StringValue getParameterValue(final String _name)
    {
        final List<StringValue> values = this.parameters.get(_name);
        return (values != null && !values.isEmpty()) ? values.get(0)
                        : StringValue.valueOf((String) null);
    }
Returns single value for parameter with specified name. This method always returns non-null
result even if the parameter does not exist.

@param _name parameter name
@return {@link StringValue} wrapping the actual value