mySQL Database Migration fails due to "null" character in Stash table

Stash could not be migrated to the new database. Some data may have already been written to the new database leaving it in an inconsistent state. You will need to empty or recreate the new database before trying again.
	com.atlassian.stash.internal.maintenance.migration.DatabaseMigrationTask.run(DatabaseMigrationTask.java:44)
	com.atlassian.stash.internal.maintenance.DefaultMaintenanceTaskMonitor.run(DefaultMaintenanceTaskMonitor.java:172)
	java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	...
Failed to execute change: Insert Row; nested exception is org.postgresql.util.PSQLException: ERROR: null value in column "from_branch_name" violates not-null constraint
  Detail: Failing row contains (1, 0, 1, 0, 2014-12-29 22:36:48.817+08, 2014-12-29 22:36:48.817+08, 1, 1, refs/heads/null, refs/heads/master, null, master, 8e33651530fffc4fa06bd912396b7e118af02df3, d88a6550790e4aff0538508675565be6ec9e97e0, null, 2).
	com.atlassian.stash.internal.backup.liquibase.DefaultLiquibaseDao.insert(DefaultLiquibaseDao.java:281)
	com.atlassian.stash.internal.backup.liquibase.DatabaseUpdater.endElement(DatabaseUpdater.java:81)
	org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source)
	...
ERROR: null value in column "from_branch_name" violates not-null constraint
  Detail: Failing row contains (1, 0, 1, 0, 2014-12-29 22:36:48.817+08, 2014-12-29 22:36:48.817+08, 1, 1, refs/heads/null, refs/heads/master, null, master, 8e33651530fffc4fa06bd912396b7e118af02df3, d88a6550790e4aff0538508675565be6ec9e97e0, null, 2).
	org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2102)
	org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1835)
	org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257)
	...