Remove spaces on new line, but keep the line - vb.net

Question

I wish to remove spaces from lines that doesn't contain text, but not remove the line. Since a space character can be hard to identify, I will replace the space character with the "#" (hastag character) to showcase the example easier. The string looks something like this:
"This is
########a long string
with many lines
#######
and the above is empty
####this is empty
#############
#######hello"
I wish that the output would remove the spaces on the lines that only contains the space character. I am still using the "#" (hastag character) to showcase the spaces. The final output should look like this:
"This is
########a long string
with many lines
and the above is empty
####this is empty
#######hello"
Without the hashtag character acting as the space character, the expected output should look like this:
"This is
a long string
with many lines
and the above is empty
this is empty
hello"
So to fully clarify, I wish to remove space characters on a line that doesn't contain text, but not remove the line.

Answer 1

Using your example with octothorpes (yet another name for #) and replacing them with spaces in the code, we can use the String.IsNullOrWhiteSpace function to check for such lines and replace them with empty strings:
Module Module1
Sub Main()
Dim s = "This is
########a long string
with many lines
#######
and the above is empty
####this is empty
#############
#######hello"
s = s.Replace("#", " ")
Dim t = String.Join(vbCrLf, s.Split({vbCrLf}, StringSplitOptions.None).
Select(Function(a) If(String.IsNullOrWhiteSpace(a), "", a)))
Console.WriteLine(t)
Console.ReadLine()
End Sub
End Module
Outputs:
This is
a long string
with many lines
and the above is empty
this is empty
hello

Answer 2

Use the following code:
Dim container As String = IO.File.ReadAllText("test.txt")
container = container.Replace(vbNewLine, vbCr).Replace(vbLf, vbCr)
Do While container.Contains(vbCr & vbCr)
container = container.Replace(vbCr & vbCr, vbCr)
Loop
If container.StartsWith(vbCr) Then container = container.TrimStart(Chr(13))
container = container.Replace(vbCr, vbNewLine)
IO.File.WriteAllText("test.txt", container)
It'll trim all the empty new lines and override the file (before vs. after):
Note: If you want to remove the hashes and replace that with white spaces too, just use the following:
Dim container2 As String =
My.Computer.FileSystem.ReadAllText("test.txt").Replace("#", " ")
IO.File.WriteAllText("test.txt", container2)

Answer 3

Try this
Dim myString = "your multiline string here"
Dim finalString As String
For each line In myString.Split(CChar(vbNewLine))
finalstring &= line.Trim() & vbNewLine
Next