Dynamically create a Expression, Define the parameter of the Expression as below

var parameter = Expression.Parameter(typeof(T));

then pass this expression to MongoQueryable.Where function

call Count or ToList

reported the below exception

Value cannot be null.
Parameter name: itemName

on the other hand, if i declare the parameter of the expression as below

var parameter = Expression.Parameter(typeof(T),"item");

then the linq expression can be successfully transformed to mongodb query

while transform the linq expression to mongodb query, why does the parameter name is required? when it comes to dynamically generated expression people usually use anonymous parameter and the exception message does not explicitly indicate the parameter expression need a name.