Find branch by name

import com.atlassian.bitbucket.repository.RefService
import com.atlassian.bitbucket.repository.Repository
import com.atlassian.bitbucket.repository.ResolveRefRequest
import com.atlassian.sal.api.component.ComponentLocator
import com.onresolve.scriptrunner.parameters.annotation.RepositoryPicker
import com.onresolve.scriptrunner.parameters.annotation.ShortTextInput

import static com.atlassian.bitbucket.repository.StandardRefType.BRANCH

@RepositoryPicker(label = "Repository", description = "Enter the repository name")
Repository repository

@ShortTextInput(label = "Branch", description = "Enter the branch name")
String branchName

def refService = ComponentLocator.getComponent(RefService)

refService.resolveRef(new ResolveRefRequest.Builder(repository).with {
    type(BRANCH)
    refId("refs/heads/${branchName}")
}.build())