Add getParent method for Commit objects
Add getParent method for Commit objects

Add method to retrieve a given parent (not ancestor) of a commit object.
If the commit doesn't have the requested parent return null.

abecerramatias/GitBranching,iambocai/learnGitBranching,xumeng/learnGitBranching,kpchen/learnGitBranching,HoldenMills/learnGitBranching,alexeiberkov/learnGitBranching,yyn835314557/learnGitBranching,bopo/learnGitBranching,edombowsky/learnGitBranching,hoharu/learnGitBranching,Maximaximum/learnGitBranching,resource11/learnGitBranching,behind2/learnGitBranching,resource11/learnGitBranching,Hydex/learnGitBranching,kaaass/learnGitBranching,ranjith068/learnGitBranching,xumeng/learnGitBranching,hugo-/learnGitBranching,YihanWang2015/learnGitBranching,julie1013/learnGitBranching,jiyiren/learnGitBranching,WilBeCoding/learnGitBranching,Maximaximum/learnGitBranching,luthfi401/learnGitBranching,USIU-Hackathon/learnGitBranching,DD-L/learnGitBranching,linglaiyao1314/learnGitBranching,YihanWang2015/learnGitBranching,lxbyes/learnGitBranching,pcottle/learnGitBranching,USIU-Hackathon/learnGitBranching,HoldenMills/learnGitBranching,ZeroDragon/learnGitBranching,lxbyes/learnGitBranching,abecerramatias/GitBranching,alskjstl/learnGitBranching,bopo/learnGitBranching,ranjith068/learnGitBranching,julie1013/learnGitBranching,myopensrc/learnGitBranching,thy09/learnGitBranching,behind2/learnGitBranching,lichenbuliren/learnGitBranching,alexeiberkov/learnGitBranching,thy09/learnGitBranching,iambocai/learnGitBranching,edombowsky/learnGitBranching,william0503/learnGitBranching,hoharu/learnGitBranching,tzq668766/learnGitBranching,myopensrc/learnGitBranching,andriymoroz/learnGitBranching,pcottle/learnGitBranching,andriymoroz/learnGitBranching,gdseller/learnGitBranching,codevlabs/learnGitBranching,Haemaru/learnGitBranching,luthfi401/learnGitBranching,pcottle/learnGitBranching,Haemaru/learnGitBranching,tzq668766/learnGitBranching,gcbeyond/learnGitBranching,gdseller/learnGitBranching,linglaiyao1314/learnGitBranching,lichenbuliren/learnGitBranching,codevlabs/learnGitBranching,kaaass/learnGitBranching,hugo-/learnGitBranching,Hydex/learnGitBranching,WilBeCoding/learnGitBranching,DD-L/learnGitBranching,alskjstl/learnGitBranching,yyn835314557/learnGitBranching,william0503/learnGitBranching,jiyiren/learnGitBranching,gcbeyond/learnGitBranching,kpchen/learnGitBranching