I suggest you use a conditional show. This can be done for the whole chart (see General tab) or for individual expressions (see top-right in the Expression tab). Inside those fields add an expression that that results in either "true" or "false".
If you are going to use conditional show in the general tab, be sure to also edit the error message (see button at the bottom of the general tab) and change it into something that tells your user what he/she is supposed to do to get results in the chart.
You could use a calculation condition (on the chart properties | general):
If you need a selection in all 3:
=GetSelectedCount(datefield) > 0 And GetSelectedCount([sales person field]) > 0 And GetSelectedCount(itemfield) > 0
If you need a selection in any 1:
=GetSelectedCount(datefield) > 0 Or GetSelectedCount([sales person field]) > 0 Or GetSelectedCount(itemfield) > 0