Sets a value of the first X property named x_name in icalcomp, if any such already exists, or adds a new
property with this name and value.
As a special case, if value is null, then removes the first X property named x_name
from icalcomp instead.
| icalcomp |
an Component |
| x_name |
name of the X property |
| value |
a value to set, or null |