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NullException

NullException()

An attempted access to a Nullable with no defined value.

Examples

In the Julia programming language, the function NullException() is used to handle attempted access to a Nullable with no defined value. It throws an exception when there is an attempt to access the value of a Nullable object that is set to null.

Common examples of its use:

1. Handle Nullable access attempt:

   julia> x = Nullable{Int}(null);
   julia> try
             value = x[]
         catch ex
             if ex isa NullException
                 println("Error: Nullable value is null.")
             end
         end
   Error: Nullable value is null.

   In this example, x is a Nullable object with no defined value. The try-catch block is used to catch the NullException and handle the error appropriately.

2. Avoid accessing Nullable value without checking:

   julia> y = Nullable{String}("Hello");
   julia> if isnull(y)
             println("Value is null.")
         else
             println("Value is: ", y[])
         end
   Value is: Hello

   This example checks if the Nullable value is null using the isnull function before accessing the value using y[]. It prevents a potential NullException by ensuring that the value is not null before accessing it.

Common mistake example:

julia> z = Nullable{Float64}(0.0);
julia> value = z[]
ERROR: NullException: NullException()

In this example, the NullPointerException is thrown because the z object is set to null. It's crucial to check for null values before attempting to access the value to avoid this error.

See Also

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