Keywords with 0 occurrences

[jmartinm]

After running arXiv:1707.00470 through the classifier, the output includes a keyword with 0 occurrences:

"core_keywords": [
{
"keyword": "field theory, topological",
"number": 1
},
{
"keyword": "supersymmetry",
"number": 0
}
],
"field_codes": [],
"filtered_core_keywords": [
{
"keyword": "field theory, topological",
"number": 1
},
{
"keyword": "supersymmetry",
"number": 0
}
]