Properties not showing in Age Viewer for any graph

### Describe the bug
When I navigate to the Age Viewer page for any graph, the properties section is blank, even though there are nodes in the graph with properties.

### To Reproduce

Open the Age Viewer for any graph.
Navigate to the Properties section.
Observe that the section is blank, even though there are nodes in the graph with properties.
### Expected behavior
When I navigate to the Age Viewer page for a specific graph, the properties section should show the properties of nodes in the graph.

### Screenshots
N/A

### Desktop (please complete the following information):

OS: macOS 10.15.7
Browser: Chrome 90.0.4430.212
Version: N/A
### Additional context
I've tried to track down the source of the problem, and it seems that the getPropertyKeys() function in the age-viewer/backend/src/services directory may not be responding correctly. When I call the function directly, it doesn't seem to be returning any results.

Any help or guidance on how to resolve this issue would be greatly

Start by searching age-viewer/backend/src/services for getPropertyKeys() and trace how its result reaches the Age Viewer Properties section. Reproduce the issue with a graph containing node properties, then verify that the section displays those properties when the function returns data.

Written by the indexing model from the issue text.