DuckDuckGo returns 500 if user agent starts with "Java"

$ curl --head --user-agent "NotJava" https://duckduckgo.com/
HTTP/2 200
server: nginx
date: Sat, 30 May 2020 19:52:48 GMT
content-type: text/html; charset=UTF-8
content-length: 5425
vary: Accept-Encoding
etag: "5ed15798-1531"
strict-transport-security: max-age=31536000
x-frame-options: SAMEORIGIN
content-security-policy: default-src https: blob: data: 'unsafe-inline' 'unsafe-eval'; frame-ancestors 'self'
x-xss-protection: 1;mode=block
x-content-type-options: nosniff
referrer-policy: origin
expect-ct: max-age=0
expires: Sat, 30 May 2020 19:52:47 GMT
cache-control: no-cache
accept-ranges: bytes

$ curl --head --user-agent "Java/14.0.1" https://duckduckgo.com/
HTTP/2 500
server: nginx
date: Sat, 30 May 2020 19:52:56 GMT
content-type: text/html; charset=UTF-8
content-length: 170
x-xss-protection: 1;mode=block
x-content-type-options: nosniff
referrer-policy: origin
expect-ct: max-age=0

$ curl --head --user-agent "Java" https://duckduckgo.com/
HTTP/2 500
server: nginx
date: Sat, 30 May 2020 19:53:03 GMT
content-type: text/html; charset=UTF-8
content-length: 170
x-xss-protection: 1;mode=block
x-content-type-options: nosniff
referrer-policy: origin
expect-ct: max-age=0