Custom .bst file : Does not process entries of type "@book"

Question

I have created a custom .bst file using makebst such that it is as per my univeristy PhD guidelines. When I run BibTex, it works perfectly for articles, conference proceedings etc. cited. However BibTeXfails when I am citing a book. The error I get is

 This is BibTeX, Version 0.99d (TeX Live 2015)
 The top-level auxiliary file: example.aux
 The style file: thbibstyle.bst
 Database file #1: books.bib
 You can't pop an empty literal stack for entry Arnett96
 while executing---line 1720 of file thbibstyle.bst
 You can't pop an empty literal stack for entry Spitzer78
 while executing---line 1720 of file thbibstyle.bst

An example .tex file is as follows:

\documentclass[a4paper,11pt]{tanvirTU}
\begin{document}
\title{Title}
\maketitle
Read \cite{Spitzer78, Arnett96}
 \bibliography{books}
  \bibliographystyle{thbibstyle}
\end{document}

Here is my .bst file: thbibstyle

Also the bibliography entry are as follows

@BOOK{Spitzer78,
   author = {{Spitzer}, L.},
    title = "{Physical processes in the interstellar medium}",
publisher = {New York Wiley-Interscience, 1978.~333 p.},
    year = 1978,
   adsurl = {http://adsabs.harvard.edu/cgi-bin/nph-bib_query?  bibcode=1978ppim.book.....S&db_key=AST},
 adsnote = {Provided by the Smithsonian/NASA Astrophysics Data     System}
}

  @BOOK{Arnett96,
    author = {{Arnett}, D.},
    title = "{Supernovae and Mucleosynthesis: An Investigation of the History of Matter from the Big Bang to the Present}",
    publisher = {Supernovae and Mucleosynthesis: An Investigation of the History of Matter, from the Big Bang to the Present, by D.~Arnett.~Princeton: Princeton University Press, 1996.},
     year = 1996,
    adsurl = {http://adsabs.harvard.edu/abs/1996snih.book.....A},
   adsnote = {Provided by the SAO/NASA Astrophysics Data System}
   }

Also the document class is customized which is: tanvirTU

Can anyone tell me why this is happening and how to fix it?

For a solution, please refer to this
Debugging a custom-bib bst file that crashes on book items