Some translations such as the ESV supply an extra line at Psalm 145:13. The NASB and NKJV side with the KJV in not including this extra line. The argument for inclusion is that Psalm 145 is an acrostic poem (i.e. a poem with each line beginning with each letter of the Hebrew alphabet) and the Masoretic text is supposedly missing the line that ought to start with נ (Nun). John Gill describes that it is not atypical of an acrostic poem to be missing some lines:
"Nor is the order always strictly observed in alphabetical psalms; in the thirty-seventh psalm the letter "ain" is wanting, and three in the twenty-fifth psalm. The Septuagint, Vulgate Latin, Syriac, Arabic, and Ethiopic versions, supply this defect here, by inserting these words, "the Lord is faithful in all his words, and holy in all his works", as if they were begun with the word Nman, but they seem to be taken from Ps 145:17, with a little alteration" (Psalm 145:13, Exposition of the Entire Bible).
Read more articles from: The King James Version is Demonstrably InerrantAlso read: Masoretic Readings Defended