Standard input is empty

NULL                   package:base                    R Documentation

_T_h_e _N_u_l_l _O_b_j_e_c_t

_D_e_s_c_r_i_p_t_i_o_n:

     ‘NULL’ represents the null object in R: it is a reserved word.
     NULL is often returned by expressions and functions whose value is
     undefined: it is also used as the empty pairlist.

     ‘as.null’ ignores its argument and returns the value ‘NULL’.

     ‘is.null’ returns ‘TRUE’ if its argument is ‘NULL’ and ‘FALSE’
     otherwise.

_U_s_a_g_e:

     NULL
     as.null(x, ...)
     is.null(x)
     
_A_r_g_u_m_e_n_t_s:

       x: an object to be tested or coerced.

     ...: ignored.

_N_o_t_e:

     ‘is.null’ is a primitive function.

_R_e_f_e_r_e_n_c_e_s:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_.  Wadsworth & Brooks/Cole.

_E_x_a_m_p_l_e_s:

     is.null(list())    # FALSE (on purpose!)
     is.null(integer(0))# F
     is.null(logical(0))# F
     as.null(list(a=1,b='c'))