Don't add newlines if there are is no output

isort/output.py

@@ -148,43 +148,46 @@ def sorted_imports(
         output_at = parsed.import_index
     formatted_output[output_at:0] = output
 
-    imports_tail = output_at + len(output)
-    while [
-        character.strip() for character in formatted_output[imports_tail : imports_tail + 1]
-    ] == [""]:
-        formatted_output.pop(imports_tail)
-
-    if len(formatted_output) > imports_tail:
-        next_construct = ""
-        tail = formatted_output[imports_tail:]
-
-        for index, line in enumerate(tail):
-            should_skip, in_quote, *_ = parse.skip_line(
-                line,
-                in_quote="",
-                index=len(formatted_output),
-                section_comments=config.section_comments,
-                needs_import=False,
-            )
-            if not should_skip and line.strip():
-                if (
-                    line.strip().startswith("#")
-                    and len(tail) > (index + 1)
-                    and tail[index + 1].strip()
-                ):
-                    continue
-                next_construct = line
-                break
-            if in_quote:
-                next_construct = line
-                break
-
-        if config.lines_after_imports != -1:
-            formatted_output[imports_tail:0] = ["" for line in range(config.lines_after_imports)]
-        elif extension != "pyi" and next_construct.startswith(STATEMENT_DECLARATIONS):
-            formatted_output[imports_tail:0] = ["", ""]
-        else:
-            formatted_output[imports_tail:0] = [""]
+    if output:
+        imports_tail = output_at + len(output)
+        while [
+            character.strip() for character in formatted_output[imports_tail : imports_tail + 1]
+        ] == [""]:
+            formatted_output.pop(imports_tail)
+
+        if len(formatted_output) > imports_tail:
+            next_construct = ""
+            tail = formatted_output[imports_tail:]
+
+            for index, line in enumerate(tail):
+                should_skip, in_quote, *_ = parse.skip_line(
+                    line,
+                    in_quote="",
+                    index=len(formatted_output),
+                    section_comments=config.section_comments,
+                    needs_import=False,
+                )
+                if not should_skip and line.strip():
+                    if (
+                        line.strip().startswith("#")
+                        and len(tail) > (index + 1)
+                        and tail[index + 1].strip()
+                    ):
+                        continue
+                    next_construct = line
+                    break
+                if in_quote:
+                    next_construct = line
+                    break
+
+            if config.lines_after_imports != -1:
+                formatted_output[imports_tail:0] = [
+                    "" for line in range(config.lines_after_imports)
+                ]
+            elif extension != "pyi" and next_construct.startswith(STATEMENT_DECLARATIONS):
+                formatted_output[imports_tail:0] = ["", ""]
+            else:
+                formatted_output[imports_tail:0] = [""]
 
     if parsed.place_imports:
         new_out_lines = []