added NaN test for if_else
added NaN test for inv
added NaN test for inv_cloglog
added NaN test for inv_logit
added NaN test for inv_sqrt
added NaN test for inv_square
added NaN test for inverse_softmax
added NaN test for is_uninitialized
added NaN test for lbeta
added NaN test for lgamma
added NaN test for lmgamma
added NaN test for log1m
added NaN test for log1m_exp
added NaN test for log1m_inv_logit
added NaN test for log1p
added NaN test for log1p_exp
added NaN test for log2
added NaN test for log_diff_exp
added NaN test for log_falling_factorial
added NaN test for log_inv_logit