Undefined method `fileEncoding' in (Xcodeproj::Project::Object::PBXFileReference)

I am getting 'file_ref.fileEncoding - undefined method error.

I am using Xcode 8.3.3 and xcodeproj --version 1.5.2
Can someone suggest a way to fix it ?

Here's the part of the code...

src.files.each do |f|
file_ref = proj.new(Xcodeproj::Project::Object::PBXFileReference)
file_ref.name = f.file_ref.name
file_ref.path = f.file_ref.path
file_ref.source_tree = f.file_ref.source_tree
file_ref.last_known_file_type = f.file_ref.last_known_file_type
**file_ref.fileEncoding = f.file_ref.fileEncoding**
begin
file_ref.move(f.file_ref.parent)
rescue
end