| Class | BadBranchMergeProposalSearchContext | The context is not valid for a branch merge proposal search. |
| Class | BadStateTransition | The user requested a state transition that is not possible. |
| Class | BranchCreationException | Base class for branch creation exceptions. |
| Class | BranchHasPendingWrites | Raised if the branch can't be processed because a write is pending. |
| Class | BranchTargetError | Raised when there is an error determining a branch target. |
| Class | CannotDeleteBranch | The branch cannot be deleted at this time. |
| Class | BranchCreationForbidden | A Branch visibility policy forbids branch creation. |
| Class | BranchTypeError | An operation cannot be performed for a particular branch type. |
| Class | InvalidBranchException | Base exception for an error resolving a branch for a component. |
| Class | CannotHaveLinkedBranch | Raised when we try to get the linked branch for a thing that can't. |
| Class | CannotUpgradeBranch | "Made for subclassing. |
| Class | AlreadyLatestFormat | Raised on attempt to upgrade a branch already in the latest format. |
| Class | CannotUpgradeNonHosted | Raised on attempt to upgrade a non-Hosted branch. |
| Class | UpgradePending | Raised on attempt to upgrade a branch already in the latest format. |
| Class | ClaimReviewFailed | The user cannot claim the pending review. |
| Class | InvalidBranchMergeProposal | Raised during the creation of a new branch merge proposal. |
| Class | InvalidNamespace | Raised when someone tries to lookup a namespace with a bad name. |
| Class | NoLinkedBranch | Raised when there's no linked branch for a thing. |
| Class | NoSuchBranch | Raised when we try to load a branch that does not exist. |
| Class | StaleLastMirrored | Raised when last_mirrored_id is out of date with on-disk value. |
| Class | PrivateBranchRecipe | Undocumented |
| Class | PrivateGitRepositoryRecipe | Undocumented |
| Class | ReviewNotPending | The requested review is not in a pending state. |
| Class | UpdatePreviewDiffNotReady | Raised if the preview diff is not ready to run. |
| Class | UserHasExistingReview | The user has an existing review. |
| Class | UserNotBranchReviewer | The user who attempted to review the merge proposal isn't a reviewer. |
| Class | WrongBranchMergeProposal | The comment requested is not associated with this merge proposal. |
| Class | UnknownBranchTypeError | Raised when the user specifies an unrecognized branch type. |
| Class | BranchHostingFault | Raised when there is a fault fetching information about a branch. |
| Class | BranchFileNotFound | Raised when a file does not exist in a branch. |
| Class | GitRepositoryCreationException | Base class for Git repository creation exceptions. |
| Class | GitRepositoryExists | Raised when creating a Git repository that already exists. |
| Class | CannotDeleteGitRepository | The Git repository cannot be deleted at this time. |
| Class | GitRepositoryCreationForbidden | A visibility policy forbids Git repository creation. |
| Class | GitRepositoryCreatorNotMemberOfOwnerTeam | Git repository creator is not a member of the owner team. |
| Class | GitRepositoryCreatorNotOwner | A user cannot create a Git repository belonging to another user. |
| Class | GitRepositoryCreationFault | Raised when there is a hosting fault creating a Git repository. |
| Class | GitRepositoryScanFault | Raised when there is a fault scanning a repository. |
| Class | GitRepositoryBlobNotFound | Raised when a blob does not exist in a repository. |
| Class | GitRepositoryBlobUnsupportedRemote | Raised when trying to fetch a blob from an unsupported remote host. |
| Class | GitRepositoryDeletionFault | Raised when there is a fault deleting a repository. |
| Class | GitTargetError | Raised when there is an error determining a Git repository target. |
| Class | NoSuchGitRepository | Raised when we try to load a Git repository that does not exist. |
| Class | NoSuchGitReference | Raised when we try to look up a Git reference that does not exist. |
| Class | GitDefaultConflict | Raised when trying to set a Git repository as the default for |
| Class | CannotModifyNonHostedGitRepository | Raised when trying to modify a non-hosted Git repository. |
| Class | CodeImportAlreadyRequested | Raised when the user requests an import that is already requested. |
| Class | CodeImportInvalidTargetType | Raised for code imports with an invalid target for their type. |
| Class | TooNewRecipeFormat | The format of the recipe supplied was too new. |
| Class | RecipeBuildException | Undocumented |
| Class | BuildNotAllowedForDistro | A build was requested against an unsupported distroseries. |
| Class | DiffNotFound | A IPreviewDiff with the timestamp was not found. |