Exception thrown if trying to validate a file that has empty whitespace followed after the escape character

[rcjsuen]

FROM alpine
COPY a b \
\ 
/dir

$ docker run -v `pwd`/Dockerfile:/Dockerfile rcjsuen/dockerfile-utils lint /Dockerfile
/dockerfile-utils/node_modules/dockerfile-ast/node_modules/vscode-languageserver-types/lib/umd/main.js:54
                throw new Error("Range#create called with invalid arguments[" + one + ", " + two + ", " + three + ", " + four + "]");
                ^

Error: Range#create called with invalid arguments[null, [object Object], undefined, undefined]
    at Object.create (/dockerfile-utils/node_modules/dockerfile-ast/node_modules/vscode-languageserver-types/lib/umd/main.js:54:23)
    at Copy.getArgumentsRanges (/dockerfile-utils/node_modules/dockerfile-ast/lib/instruction.js:82:81)
    at Copy.getArgumentsContent (/dockerfile-utils/node_modules/dockerfile-ast/lib/instruction.js:163:27)
    at Validator.checkJSONQuotes (/dockerfile-utils/lib/dockerValidator.js:1043:39)
    at Validator.validateInstruction (/dockerfile-utils/lib/dockerValidator.js:700:26)
    at Validator.validate (/dockerfile-utils/lib/dockerValidator.js:309:18)
    at Object.validate (/dockerfile-utils/lib/main.js:140:22)
    at validate (/dockerfile-utils/bin/dockerfile-utils:161:39)
    at Object.<anonymous> (/dockerfile-utils/bin/dockerfile-utils:35:5)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)