@Override
    public final SourceLocation getSourceLocation() {
        return sourceLocation;
    }
Casts the current node to a {@code NullNode}, throwing
{@link ExpectationNotMetException} when the node is the wrong type.

@param message Error message supplier.
@return Returns a null node.
@throws ExpectationNotMetException when the node is the wrong type.
smithy-model/src/main/java/software/amazon/smithy/model/node/Node.java