fix(oas): prevent duplicate null values in enum array [ISSUE-271]#272

Drew-Kimberly wants to merge 3 commits intostoplightio:masterstoplightio/http-spec:masterfrom

Drew-Kimberly:fix/ISSUE-271/null-value-in-enum-arrayDrew-Kimberly/stoplight-http-spec:fix/ISSUE-271/null-value-in-enum-arrayCopy head branch name to clipboard