Toolshed Error displaying tool: list indices must be integers, not str.

1. Goto https://toolshed.g2.bx.psu.edu/view/peterjc/seq_filter_by_id/141612f8c3e3 or
2. Scroll down to the "Contents of this repository" section
3. Expand the "Valid tools" section
4. Click on "Select Sequences by ID"

**Actual result:**

Red error message:

*Error displaying tool, probably due to a problem in the tool config. The exception is: list indices must be integers, not str.*

**Expected result:**

A preview of the tool, which still works on the Test Tool Shed - see https://testtoolshed.g2.bx.psu.edu/view/peterjc/seq_select_by_id/c7d51db59082

Start by reproducing the error at the linked Toolshed repository and compare it with the Test Tool Shed preview. Trace the tool display and configuration handling for the “Valid tools” entry; done means clicking “Select Sequences by ID” shows a tool preview instead of the list-index error.

Written by the indexing model from the issue text.