Update run_black_on_git_diff_adds.sh

Can now handle if a file is deleted

run_black_on_git_diff_adds.sh

@@ -18,13 +18,19 @@ echo "looking for diff at ${github_pr_url}"
 curl --request GET --url ${github_pr_url} --header "authorization: Bearer ${GITHUB_TOKEN}" --header "Accept: application/vnd.github.v3.diff" > github_diff.txt
 diff_length=`wc -l github_diff.txt`
 echo "approximate diff size: ${diff_length}"
-python_files=`cat github_diff.txt | grep -E -- "\+\+\+ |\-\-\- " | awk '{print $2}' | grep -Po -- "(?<=[ab]/).+\.py$"`
-echo "python files edited in this PR: ${python_files}"
+python_files=`cat github_diff.txt | grep -E -- "\+\+\+" | awk '{print $2}' | grep -Po -- "(?<=[ab]/).+\.py$"`
 
-if [[ -z "${LINE_LENGTH}" ]]; then
-    line_length=130
+if [ ! "$python_files" ];then
+   echo "no python files to check"
 else
-    line_length="${LINE_LENGTH}"
-fi
+    echo "python files edited in this PR: ${python_files}"
+
+    if [[ -z "${LINE_LENGTH}" ]]; then
+    line_length=130
+    else
+        line_length="${LINE_LENGTH}"
+    fi
+
+    black --line-length ${line_length} --check ${python_files}
 
-black --line-length ${line_length} --check ${python_files}
+fi