• Version of JMockit that was used:

OpenJDK 1.8.0_232, JUnit 4.12, JMockit 1.48

• Description of the problem or enhancement request:

Below example JUnit code snippet fails with an java.lang.IllegalArgumentException

final List<String[]> commandArrays = new ArrayList<>();
new MockUp<ProcessBuilder>() {
  @Mock
  public ProcessBuilder command(Invocation inv, String... command) {
    commandArrays.add(command);
    inv.proceed((Object[])command);
  }
};

new ProcessBuilder().command("echo", "'Some test'");

Result:

 java.lang.IllegalArgumentException: Failure to invoke method: public java.lang.ProcessBuilder java.lang.ProcessBuilder.command(java.lang.String[])
  Caused by: java.lang.IllegalArgumentException: argument type mismatch

While faking ProcessBuilder via MockUp is probably a bad idea and mocking should be used instead, is it an easy example to show this bug.