Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed. When a block contains a comment, this block is not considered to be empty.

The following code snippet illustrates this rule:

void doSomething() {
  for (int i = 0; i < 42; i++)        // Non-Compliant
  {
  }
  for (int i = 0; i < 42; i++);       // Compliant

  if (myVar == 4)                     // Compliant - contains a comment
  {
    // Do nothing because of X and Y
  }
  else                                // Compliant
  {
    doSomething();
  }

  try                                 // Non-Compliant
  {
  }
  catch (Exception e)                 // Compliant
  {
    // Ignore
  }
}