2. Additionally, the defendant admitted all the circumstances of the robbery above set out in a signed statement. This was referred to by the court as an "incriminating statement," "statement" or "an alleged statement" in a lengthy and correct charge on the admissibility and evidentiary effect of such a statement (which in a preliminary statement he also once referred to as confession). The document was held admissible after a Jackson-Denno hearing, but, the appellant enumerates error on the failure of the trial court to specifically instruct the jury without request that "an uncorroborated confession was not of itself sufficient in law to warrant a conviction," citing Lucas v. State, 110 Ga. 756 (4) (36 SE 87) (1900). Lucas states a salutory rule which should always be applied where "the case, at best, is close and doubtful, and it is by no means clear that the evidence warranted a conviction." Id. p. 759. In cases not fitting this definition it is obiter. Plummer v. State, 27 Ga. App. 185, 187 (108 SE 128) (1921), and see Brantley v. State, 154 Ga. 80 (113 SE 200) (1922); Simonton v. State, 151 Ga. App. 431 (7) (260 SE2d 487) (1979). No reversible error appears.