Possible bug: Length of coverage does not always match number of source lines in file

[DilumAluthge]

Here is a minimal (albeit contrived) example.

In example_1.jl, the length of coverage[1].coverage is equal to the length of split(coverage[1].source, '\n').

However, in example_2.jl, the length of coverage[2].coverage is equal to the length of split(coverage[2].source, '\n')

Contents of example_1.jl:

function foo(x)
    x + x
end

foo(1)

Contents of example_2.jl:

using Test

@testset begin
    @test 1 == 1
    @test 2 == 2
end

Julia session:

shell> ls
example_1.jl	example_2.jl

shell> cat example_1.jl
function foo(x)
    x + x
end

foo(1)

shell> cat example_2.jl
using Test

@testset begin
    @test 1 == 1
    @test 2 == 2
end

julia> split(read("example_1.jl", String), '\n')
6-element Array{SubString{String},1}:
 "function foo(x)"
 "    x + x"
 "end"
 ""
 "foo(1)"
 ""

julia> split(read("example_2.jl", String), '\n')
7-element Array{SubString{String},1}:
 "using Test"
 ""
 "@testset begin"
 "    @test 1 == 1"
 "    @test 2 == 2"
 "end"
 ""

shell> julia --code-coverage example_1.jl

shell> julia --code-coverage example_2.jl
Test Summary: | Pass  Total
test set      |    2      2

julia> using Coverage

julia> coverage = process_folder(pwd());
[ Info: Coverage.process_folder: Searching /Users/dilum/Downloads/example for .jl files...
[ Info: Coverage.process_file: Detecting coverage for /Users/dilum/Downloads/example/example_1.jl
[ Info: Coverage.process_cov: processing /Users/dilum/Downloads/example/example_1.jl.82432.cov
[ Info: Coverage.process_file: Detecting coverage for /Users/dilum/Downloads/example/example_2.jl
┌ Info: Coverage.process_cov: Coverage file(s) for /Users/dilum/Downloads/example/example_2.jl do not exist.
└ Assuming file has no coverage.

julia> split(coverage[1].source, '\n')
6-element Array{SubString{String},1}:
 "function foo(x)"
 "    x + x"
 "end"
 ""
 "foo(1)"
 ""

julia> coverage[1].coverage
6-element Array{Union{Nothing, Int64},1}:
  nothing
 2
  nothing
  nothing
  nothing
  nothing

julia> split(coverage[2].source, '\n')
7-element Array{SubString{String},1}:
 "using Test"
 ""
 "@testset begin"
 "    @test 1 == 1"
 "    @test 2 == 2"
 "end"
 ""

julia> coverage[2].coverage
6-element Array{Union{Nothing, Int64},1}:
 nothing
 nothing
 nothing
 nothing
 nothing
 nothing