Skip lines with transformLine

I am wondering if there any way I am missing of skipping lines when using transformLine?

The last line in the closure is the line value written. Looking at a SSCCE, we have file1.txt with 4 lines:

line1
line2
line11
line22

I want to produce the file2.txt with 2 lines:

line1
line11

import java.util.regex.Matcher
import java.io.Reader
import java.io.Writer

def file1 = /C:\Workspace\Test\file1.txt/
def file2 = /C:\Workspace\Test\file2.txt/
def writeLine
FileWriter writeFile = new FileWriter(file2)
                new FileReader(file1).transformLine(writeFile) { line ->
                    Matcher m1 = line =~ /line1\d*/
                    writeLine = ''
                    if (m1.matches()) {
                         writeLine = line                  
                    }
                    writeLine
                }

will give:

line1
<blank line>
line11
<blank line>

I could then reprocess the field to remove blank lines, but it would be great if there was a way of skipping lines with transformLine.