What is the subject in this sentence?
There is no form to reject.
And what type of sentence is this?
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There is an "expletive subject".
It is a bit like the word "it" in the sentence "It is raining". So what is "it"? It is a placeholder with no essential meaning, called an "expletive subject" or "pleonastic subject".
You will find out more about the expletive subject at English Language & Usage