I have one HTTP request which is responding with no content value (No response body). Is it necessary to have a content-type header specified for these kinds of responses?
A Content-Type header is applicable to a response with a body per RFC 2616:
When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type and Content- Encoding.
By extension, it's not necessary if there is no response body, as you're describing.
It is a SHOULD and not a MUST, so it is RFC-compliant to not include that header even if there is a response body:
Any HTTP/1.1 message containing an entity-body SHOULD include a
Content-Type header field defining the media type of that body.
As @Elhitch says, when the client has to guess what the Content-Type is, it's possible it will guess wrong with negative implications. But that doesn't apply to your use case of 'No content value (No response body)'.
Perhaps this article in the NetSparker knowledge base might be useful to you.
"[...] a missing Content-Type header which means that this website could be at risk of a MIME-sniffing attacks. [...] The problem arises once a website allows users to upload content which is then published on the web server. If an attacker can carry out XSS (Cross-site Scripting) attack by manipulating the content in a way to be accepted by the web application and rendered as HTML by the browser, it is possible to inject code in e.g. an image file and make the victim execute it by viewing the image.