[Python] Dataframe fill for null values - Pandas

I encounter problems trying to fill all null values on a specific column of a data frame.

Here is an example of dataframe and my expected outcome.

Example data frame:

Column_1 Column_2
F A
None B
None None
G C
None None
None D
H D


I want to get the first value from the column 1 to all null value from column 2

Expected Outcome:

Column_1 Column_2
F A
None B
None G #First value from the left column
G C
None H #First value from the left column
None D
H D


I'm getting error when I try this code.

df['Colunmn_2'].ffill(df.loc[df['Column_1'].first_valid_index(), 'Column_1'],inplace=True)

Thanks in advance!

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