Return all records when parameter is null or empty in Linq query in ASP.Net

how to filter data from linq query in c#?

if i passing value of lineid as 1 means it will return id's like 1, 11, 12

i need to return only line id which having "1" alone,

can anybody help?

string lineId = model.LineID > 0 ? model.LineID.ToString() : "";
reflist = reflist.Where(a => a.LineID.ToString().Contains(lineId.ToString())).ToList();

if i use equals means if line id is null or empty means it will not returning any data.

if null or empty means it should return all data