ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values

ERROR: UndefRefError: access to undefined reference This avoids the need to continually check for null values. However, not all object fields are references. Julia considers some types to be "plain data" raw pointer value must be called at runtime for precompilation to work (Ptr objects will turn into null pointers unless they are hidden inside an isbits object). This includes the return values of the the missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 21.1 Propagation of Missing Values