We have faced - and found - a solution to this exact problem.
Problem summary: When using parameters and calculated fields to control what data is being displayed, specifically with multi-chart dashboards, it may be possible for a given chart to have no data or multiple values (all). This leads to the title of the chart reading "All"
1) Hide titles on the sheets in the dashboard
2) Create a new sheet that has the same actions and filters applied to it
3) Set the sheet's mark type to Text
4) Add your calculated fields and other text to the Label shelf
5) Format the sheet to remove all boards
6) Place the sheet directly above the chart on the dashboard
Now when there is no data on the chart, the "title" sheet will be blank instead of reading "All."
I've posted a very simple dummy work book to show the technique here: https://public.tableausoftware.com/profile/chris.patrick#!/vizhome/BlankTitleExample/BadDashboardExample
Hope this helps!
BlankTitleExample.twbx 62.6 KB