"beginning of combat" & "declare attackers" step

[Jean le Chauve]

John Doe reported:

"beginning of combat" & "declare attackers" step should be in each turn (even if no creature can attack).
There should be still a "beginning of combat" & "declare attackers" step even if there are no creatures to attack.

506.1. The combat phase has five steps, which proceed in order: beginning of combat, declare attackers, declare blockers, combat damage, and end of combat. The declare blockers and combat damage steps are skipped if no creatures are declared as attackers or put onto the battlefield attacking (see rule 508.5). There are two combat damage steps if any attacking or blocking creature has first strike (see rule 702.7) or double strike (see rule 702.4).

As I tried to add Sentry Oak I've noticed this and now in a talk between gander and marek14 it came up again. This is from a comment I had added to Sentry Oak as I left it commented out:

"Sentry Oak\n{4W}\nCreature - Treefolk Warrior\nLRW,U\nDefender\rAt the beginning of combat on your turn, you may clash with an opponent. If you win, Sentry Oak gets +2/+0 and loses defender until end of turn.\n3/5"
"When there's no attack-able creature with it, the BeginningOfCombatStep/Combat phase becomes skipped(!) and it doesn't trigger. But if there's an attack-able creature with it, it works as it should.