fix panic with assertion when the value of the output fields are nil …

[Issif]

…and not interface{}

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area build

/area config

/area outputs

/area tests

What this PR does / why we need it:

fix panic with assertion when the value of the output fields are nil and not interface{}

2023/03/23 13:30:43 http: panic serving 127.0.0.1:45414: interface conversion: interface {} is nil, not string
goroutine 74183 [running]:
net/http.(*conn).serve.func1()
	$GOROOT/src/net/http/server.go:1854 +0xbf
panic({0x21f5840, 0xc000a163c0})
	$GOROOT/src/runtime/panic.go:890 +0x263
main.newFalcoPayload({0x7f2a4bdee318?, 0xc0006d8200})
	/home/runner/work/falcosidekick/falcosidekick/handlers.go:107 +0x1509
main.mainHandler({0x2b1d0f0, 0xc0001b28c0}, 0xc000564200)
	/home/runner/work/falcosidekick/falcosidekick/handlers.go:43 +0x286
net/http.HandlerFunc.ServeHTTP(0xc0001b28c0?, {0x2b1d0f0?, 0xc0001b28c0?}, 0x2572cf4?)
	$GOROOT/src/net/http/server.go:2122 +0x2f
net/http.(*ServeMux).ServeHTTP(0x0?, {0x2b1d0f0, 0xc0001b28c0}, 0xc000564200)
	$GOROOT/src/net/http/server.go:2500 +0x149
net/http.serverHandler.ServeHTTP({0x2b0e708?}, {0x2b1d0f0, 0xc0001b28c0}, 0xc000564200)
	$GOROOT/src/net/http/server.go:2936 +0x316
net/http.(*conn).serve(0xc0001361b0, {0x2b1e178, 0xc0007a8b10})
	$GOROOT/src/net/http/server.go:1995 +0x612
created by net/http.(*Server).Serve
	$GOROOT/src/net/http/server.go:3089 +0x5ed

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

LGTM label has been added.

Git tree hash: 23eac26418d6aad7d1ca4c99e698e4c3cbf7c313

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fjogeleit, Issif

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