Kashmiri Shaiva mystic Utpaladeva in his Shiva Stotravalli says,
This fearful world has well-nigh come to an end; the heavy dross of the mind has melted away; still there is, O Lord, not the least opening in the bolted panels of Thy city gates. 4.15
What he meant is despite getting rid of all the conditionings of the mind, he is yet to become the nectar. The commentator has commented on the verse as
The verse is suggestive of what is known in mystic circles as Sunya Bhumi. It is a negative experience and must be overcome with relentless effort combined with the Lord's grace.
Do we find the phrase in any of the scriptures or the works of scholars, mystics, acharyas, etc.? And what does the phrase connote if at all we find the phrase somewhere?