Splitting a multiline string by regex ha unwanted elements in result array

I’m trying to split a multiline string using a regex.

const regexCommitSha = RegExp(/([0-9a-f]{7})s/m)
const result = commits.split(regexCommitSha)
console.log(result)

This is my multiline string (commits):

1234567 fix: simple bug fix
apps/backend/src/lib/file.ts
1234567 fix: second bug fix
apps/backend/src/lib/file.ts
apps/frontend/src/lib/file.ts
1234567 feat: new feature
apps/frontend/src/lib/file.ts
1234567 feat: second feature
apps/frontend/src/lib/file.ts

And this is my result:

[
  '',
  '1234567',
  'fix: simple bug fixnapps/backend/src/lib/file.tsn',
  '1234567',
  'fix: second bug fixn' +
    'apps/backend/src/lib/file.tsn' +
    'apps/frontend/src/lib/file.tsn',
  '1234567',
  'feat: new featurenapps/frontend/src/lib/file.tsn',
  '1234567',
  'feat: second featurenapps/frontend/src/lib/file.ts'
]

Why do I have the empty string as first element and why do I have '1234567'-elements in my result array? As this is my splitter, I thought this is not existing in the result.

I would expect

[
  'fix: simple bug fixnapps/backend/src/lib/file.tsn',
  'fix: second bug fixn' +
    'apps/backend/src/lib/file.tsn' +
    'apps/frontend/src/lib/file.tsn',
  'feat: new featurenapps/frontend/src/lib/file.tsn',
  'feat: second featurenapps/frontend/src/lib/file.ts'
]

What am I doing wrong?