message: Change if statement syntax to use positive expressions
diff: @@ -25,17 +25,15 @@ clone() {
  # First we check if GITHUB_HEAD_REF is defined,
  # Then we check if BUILDKITE_BRANCH is defined,
  # if it isn't we can assume this is a Netlify build
  -if [ -z ${BUILDKITE_BRANCH+x} ]; then
  - if [ -z ${GITHUB_HEAD_REF+x} ]; then
  +if [ -n "$BUILDKITE_BRANCH" ]; then
  + head=$BUILDKITE_BRANCH
  +elif [ -n "$GITHUB_HEAD_REF" ]; then
  + head=$GITHUB_HEAD_REF
  +else
  # Netlify doesn't give us info about the fork so we have to get it from GitHub API
  apiEndpoint="https://api.github.com/repos/matrix-org/matrix-react-sdk/pulls/"
  apiEndpoint+=$REVIEW_ID
  head=$(curl $apiEndpoint | jq -r '.head.label')
  - else
  - head=$GITHUB_HEAD_REF
  - fi
  -else
  - head=$BUILDKITE_BRANCH
  fi
  # If head is set, it will contain on Buildkite either:
  @@ -46,7 +44,8 @@ fi
  # to determine whether the branch is from a fork or not
  BRANCH_ARRAY=(${head//:/ })
  if [[ "${#BRANCH_ARRAY[@]}" == "1" ]]; then
  - if [ -z ${BUILDKITE_BRANCH+x} ]; then
  +
  + if [ -n "$GITHUB_HEAD_REF" ]; then
  if [[ "$GITHUB_REPOSITORY" == "$deforg"* ]]; then
  clone $deforg $defrepo $GITHUB_HEAD_REF
  else
  @@ -61,9 +60,9 @@ elif [[ "${#BRANCH_ARRAY[@]}" == "2" ]]; then
  fi
  # Try the target branch of the push or PR.
  -if [ -n ${GITHUB_BASE_REF+x} ]; then
  +if [ -n $GITHUB_BASE_REF ]; then
  clone $deforg $defrepo $GITHUB_BASE_REF
  -elif [ -n ${BUILDKITE_PULL_REQUEST_BASE_BRANCH+x} ]; then
  +elif [ -n $BUILDKITE_PULL_REQUEST_BASE_BRANCH ]; then
  clone $deforg $defrepo $BUILDKITE_PULL_REQUEST_BASE_BRANCH
  fi
  