If I want to create a new dataframe sliced from my existing dataframe $"$df$"$ where any row with an entry in column "value" is removed, which of these would correctly create the new df$?$

$1.$

df$[$df$.$value.isnull$()]$

$2.$

df$\_2=$ df$[$df$.$value.isnull$()]$

$3.$

df$\_2=$ df$.$dropna$()$

$4.$

df$\_2=$ df$[$df$[\text{'}$value$\text{'}]=$ isnull$()]$