Parameter.AsString return value

[mmaso64U7Y]

Documentation says: Provides access to the string contents of the parameter.

Expected: When the string stored in the parameter is an empty string, I expect an empty string.

Current: When the string stored in the parameter is an empty string, the return value is a null reference.

Example: When I try to copy the contents from one parameter to another one, an empty string will be responsible of throwing an exception.

if (param1.StorageType == StorageType.String & param2.StorageType == StorageType.String)
{
    param2.Set(param1.AsString());
}

It also applies to AsValueString method.

Possible workaround:

param2.Set(param1.AsString() ?? "");

Note that this workaround does not solve the inconsistency in the API.

[jeremy_tammik]

Thank you for letting us know and glad to hear that you found a workaround.

[nice3point]

You need to add a parameter.HasValue check

[ricaun]

That's how string parameter works in Revit.

By default, all the string parameters do not have a value, resulting in the 'null' when using AsString. If you set the parameter to string.Empty or (string)null, the parameter gonna have value, AsString returns an empty string.

If I use the code below, I don't see an exception, the value goes to string.Empty. (Testing in Revit 2021)

var parameter = familyInstance.get_Parameter(BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS);
parameter.Set((string)null);