Git merge

Perform a git merge may generate a merge message, or not.
General, when a merge can be performed with fast-forward, no new merge commit will be generated, otherwise there will be a merge message.

*---* (master)
     \
      *---*---* (foo)

# In this scenario, merge 'foo' to 'master', will be 'fast-forward'.

*---*
     \
      *---*---* (master, foo)

*---*---* (master)
     \
      *---*---* (foo)

# Whereas this scenario a new merge commit will be generated
                ↓
*---*---*-------* (master)
     \         / 
      *---*---* (foo)