556.051. When the phrase "The defendant shall have the burden of injecting the issue" is used in the code, it means
(1) The issue referred to is not submitted to the trier of fact unless supported by evidence; and
(2) If the issue is submitted to the trier of fact any reasonable doubt on the issue requires a finding for the defendant on that issue.
(L. 1977 S.B. 60)
Missouri General Assembly