How to add a user and multi users to the People picker field in a sharepoint list programmtically

string projectMemberValue = string.Empty; try    {       //To Store Multiple users       if (spProjectListItem["ProjectMember"] != null)       projectMemberValue = spProjectListItem["ProjectMember"].ToString();       SPFieldUserValueCollection oFieldUserValueCollection = new SPFieldUserValueCollection(spDLRWeb,                                                                                                                     spProjectListItem["ProjectMember"].ToString());        spListItem["ProjectMember"] = oFieldUserValueCollection;    }  catch { } try    {       // To Store Single user.        if (spProjectListItem["ProjectOwner"] != null)        projectOwnerValue = spProjectListItem["ProjectOwner"].ToString();        SPFieldUser userOwnerField = (SPFieldUser)spDLRWeb.Lists["Projects"].Fields.GetField("ProjectOwner");        SPFieldUserValue fieldOwnerValue = (SPFieldUserValue)userOwnerField.GetFieldValue(projectOwnerValue);        projectOwner = fieldOwnerValue.User;     }  catch { }

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