A DESCRIPTION OF THE PROBLEM :
PrettyWriter::printClassLoader doesn't add a newline if the classloader is null, this causes the jfr CLI tool and also jdk.jfr.Event::toString() to print certain events slightly less pretty.

but no fear, PR248 is here: https://github.com/openjdk/jdk/pull/248

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
how to reproduce using JFR CLI:
To generate a JFR dump for testing, simply start HelloWorld.java

public class HelloWorld {
    public static void main(String[] args) {System.out.println("hello there");}
}

with
jdk-15+36/bin/java -XX:StartFlightRecording=filename=dump.jfr,dumponexit=true HelloWorld.java

now inspect the dump with
jfr print --events jdk.ModuleRequire dump.jfr

and scroll or grep to an event with "classLoader = null"

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
(PR248 applied to JDK16)
jdk16/build/linux-x86_64-server-release/jdk/bin/jfr print --events jdk.ModuleRequire dump.jfr
...
jdk.ModuleRequire {
  startTime = 16:12:43.524
  source = {
    name = "jdk.nio.mapmode"
    version = "15"
    location = "jrt:/jdk.nio.mapmode"
    classLoader = null
  }
  requiredModule = {
    name = "java.base"
    version = "15"
    location = "jrt:/java.base"
    classLoader = null
  }
}
...
ACTUAL -
(current result)
jdk-15+36/bin/jfr print --events jdk.ModuleRequire dump.jfr
...
jdk.ModuleRequire {
  startTime = 16:12:43.524
  source = {
    name = "jdk.nio.mapmode"
    version = "15"
    location = "jrt:/jdk.nio.mapmode"
    classLoader = null }
  requiredModule = {
    name = "java.base"
    version = "15"
    location = "jrt:/java.base"
    classLoader = null }
}
...

FREQUENCY : always