Getting Syntax Error in Pyspark if statement

if (df.where(col("field").isNull()).count() !=0):
  df3 = df2.join(df, on=['field'], how='outer')

elif (df.where(col("field2").isNull()).count() !=0):
  df3 = df2.join(df, on=['field2'], how='outer')

else:
  df3 = df2.join(df, on=['field3'], how='outer')

I am getting SyntaxError: invalid syntax here, would like to know how to fix it.