I have the following Makefile

~/w/i/craft-api git:develop ❯❯❯ cat Makefile                                                                                     ⏎ ✱ ◼
test:
    echo "TODO: write tests"
generate-toc:
    if ! [ -x "$(command -v doctoc)" ]; then
        echo "Missing doctoc. Run 'npm install doctoc -g' first"
    else
        doctoc ./README.md
    fi

I'm encountering this error

~/w/i/craft-api git:develop ❯❯❯ make generate-toc                                                                                  ✱ ◼
if ! [ -x "" ]; then
/bin/sh: -c: line 1: syntax error: unexpected end of file
make: *** [generate-toc] Error 2

What is incorrect in my Makefile syntax / usage?

edit 1

Adding line-continuing backslashes doesn't appear to fix the issue:

~/w/i/craft-api git:develop ❯❯❯ cat Makefile                                                                                     ⏎ ✱ ◼
test:
    echo "TODO: write tests"
generate-toc:
    if ! [ -x "$(command -v doctoc)" ]; then \
      echo "Missing doctoc. Run 'npm install doctoc -g' first" \
    else \
        doctoc ./README.md \
    fi
~/w/i/craft-api git:develop ❯❯❯ make generate-toc                                                                                  ✱ ◼
if ! [ -x "" ]; then \
      echo "Missing doctoc. Run 'npm install doctoc -g' first" \
    else \
        doctoc ./README.md \
    fi
/bin/sh: -c: line 1: syntax error: unexpected end of file
make: *** [generate-toc] Error 2