[bitbucket pipelines] allow commit arg to be optional when only pattern is passed in pipeline trigger api (#848)

* [bitbucket pipelines] allow commit arg to be optional when only pattern is passed

* remove condition to check that both are empty

* fix line break and modify doc

Co-authored-by: Arvind <arvind.kalyan@suprdaily.com>

Author: arvind-kalyan

atlassian/bitbucket/cloud/repositories/pipelines.py

@@ -21,7 +21,7 @@ def trigger(self, branch="master", commit=None, pattern=None, variables=None):
 
         1. Latest revision of a branch (specify ``branch``)
         2. Specific commit on a branch (additionally specify ``commit``)
-        3. Specific pipeline (additionally specify ``pattern``)
+        3. Specific pipeline (additionally specify ``pattern``. ``commit`` is optional here)
 
         Variables has to be a list of dictionaries:
 
@@ -48,8 +48,6 @@ def trigger(self, branch="master", commit=None, pattern=None, variables=None):
                 "hash": commit,
             }
         if pattern is not None:
-            if commit is None:
-                raise ValueError("Missing argument [commit].")
             data["target"]["selector"] = {
                 "type": "custom",
                 "pattern": pattern,