Duplicates in license detection result

The content of scanning file is:
`{ "ZPL-2.0", new LicenseData(licenseID: "ZPL-2.0", isOsiApproved: true, isDeprecatedLicenseId: false, isFsfLibre: true) }`

The license detection result is below:
```
{
"path": "test_file",
"type": "file",
"licenses": [
{
"key": "zpl-2.0",
"score": 50.0,
"name": "Zope Public License 2.0",
"short_name": "ZPL 2.0",
"category": "Permissive",
"is_exception": false,
"owner": "Zope Community",
"homepage_url": "http://www.zope.org/Resources/License/",
"text_url": "http://www.zope.org/Resources/License/",
"reference_url": "https://enterprise.dejacode.com/urn/urn:dje:license:zpl-2.0",
"spdx_license_key": "ZPL-2.0",
"spdx_url": "https://spdx.org/licenses/ZPL-2.0",
"start_line": 1,
"end_line": 1,
"matched_rule": {
"identifier": "spdx_license_id_zpl-2.0_for_zpl-2.0.RULE",
"license_expression": "zpl-2.0",
"licenses": [
"zpl-2.0"
],
"is_license_text": false,
"is_license_notice": false,
"is_license_reference": true,
"is_license_tag": false,
"matcher": "2-aho",
"rule_length": 3,
"matched_length": 3,
"match_coverage": 100.0,
"rule_relevance": 50.0
}
},
{
"key": "zpl-2.0",
"score": 50.0,
"name": "Zope Public License 2.0",
"short_name": "ZPL 2.0",
"category": "Permissive",
"is_exception": false,
"owner": "Zope Community",
"homepage_url": "http://www.zope.org/Resources/License/",
"text_url": "http://www.zope.org/Resources/License/",
"reference_url": "https://enterprise.dejacode.com/urn/urn:dje:license:zpl-2.0",
"spdx_license_key": "ZPL-2.0",
"spdx_url": "https://spdx.org/licenses/ZPL-2.0",
"start_line": 1,
"end_line": 1,
"matched_rule": {
"identifier": "spdx_license_id_zpl-2.0_for_zpl-2.0.RULE",
"license_expression": "zpl-2.0",
"licenses": [
"zpl-2.0"
],
"is_license_text": false,
"is_license_notice": false,
"is_license_reference": true,
"is_license_tag": false,
"matcher": "2-aho",
"rule_length": 3,
"matched_length": 3,
"match_coverage": 100.0,
"rule_relevance": 50.0
}
}
],
"license_expressions": [
"zpl-2.0",
"zpl-2.0"
],
"scan_errors": []
}
```

* What OS are you running on? Linux
* What version of scancode-toolkit was used to generate the scan file? 3.1.1.post848.57dab7d24
* What installation method was used to install/run scancode? source download