Closed Issue: Filter Expression required but unassigned [185]

Error:
private IEnumerable<string> DistinctFieldsInExpression(string expression)
{
// Fields should be indicated by [ ] characters.
List<string> allNames = new List<string>();
bool isField = false; // I don't think nesting is possible
List<char> currentName = new List<char>();
foreach (char current in expression) <== expression is null
/// so "Object reference not set to an instance of an object."

Steps to repoduce.
1. DemoMap
2. Add a Polygon Layer
3. Enable the Shape Editor
4. Use the move vertex tool to move a vertex.

The exception will be thrown