Wrong argument types for comparison

this is not the first time this piece of code has helped me to get rid
of a weird error:

ERROR:
Error executing code: Wrong argument types for comparison.

Stack trace:
(C) \Classes\QueryRun\next
(C) \Classes\FormDataSource\executeQuery
(C) \Forms\MyForm\Data Sources\MyFormDatasource\Methods\executeQuery - line 4
(C) \Classes\FormDataSource\linkActive
(C) \Forms\MyForm\Data Sources\MyFormDatasource\Methods\linkActive - line 3

SOLUTION:
on the form init,

public void init()
{
super();
this.query().dataSourceNo(1).clearDynalinks();
}