Fix possible crash in program construction

[andrewbranch]

Fixes #89

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Latest commit: 0055de6f0a199b69edffee695dbeeafd55d89cf2

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| Name | Type | | ------------------------- | ----- | | @arethetypeswrong/core | Patch | | @arethetypeswrong/cli | Patch | | @arethetypeswrong/history | Patch |

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