comma delimiter and space

I have a csv file and there is a problem which I need to resolve.
Column1,Column2,Colum3,Column4
,x,y,z
,d,c,v
t,l,m,n
,h,s,k
,k,,y
z,j, ,p

Now if you see column1 for row 1 and row 4 though they are null there is a space but in case of row2 and row 5 there is no space.
I want row 1 and row 4 to look like row 2 and row 5.
Also if you see row 6 column 3 it is null but it has space, however row 5 and column 3 though null doesnot have space.
Basically I want a solution whereby if a column is null then between two comma delimters there should not be any space
and this should be applicable at the first column also.Any clue guys.

sed 's/ //g' file > file

this will remove all spaces anywhere in the file.

$ cat test
Column1,Column2,Colum3,Column4
,x,y,z
,d,c,v
t,l,m,n
,h,s,k
,k,,y
z,j, ,p
$ sed 's/ //g' test
Column1,Column2,Colum3,Column4
,x,y,z
,d,c,v
t,l,m,n
,h,s,k
,k,,y
z,j,,p

Kastin
If I use 's/ //g' then all spaces will be removed
like if I have a value in a field which is like below
,xi hy,y,z
,dg hy,c,v
t,l,m,n
,h,s,k
,k,,y
z,j, ,p

I will get this

space,xihy,y,z
,dghy,c,v
t,l,m,n
space,h,s,k
,k,,y
z,j, ,p
If you see xi hy and dg hy...they become together xihy and dghy
I dont want that
not all spaces will be removed but if there is a null column
, , then it should be ,, and this should be applicable to first field also.
Sorry for any confusion. Also here when in row 1 and 4 when i try to create space in the column1 field it doesnot take in this forum ..so I wrote space there

S you need to do something like

sed 's/,  */,/g;s/  *,/,/g' 

instead.

---------- Post updated at 02:43 PM ---------- Previous update was at 02:41 PM ----------

By the way, that's two spaces before each *. Not necessary for this case and there are other ways to specify "one or more" spaces, but this is old habit and I just do it on autopilot.