Error when message trigger contains a table that is being grouped by a column

[pmallol]

Found in Version: 1.5-pre2

1. Create an Application and add a message trigger
2. Complete "When a message like this is received:" with 'hello'
3. Click on New data to create a 'Table 1'
4. Create a column on Table 1 called 'contact'
5. Drag and drop the contact pill [+1-(234)-567-8912] under the contact column of Table 1
6. Right click on 'contact' to group the table by that column
7. Save message trigger
8. Test in the sandbox

Obtained: Error: undefined methodgroup_by=' for #`