diff --git a/.gitignore b/.gitignore
index 76442a6..5603b61 100644
--- a/.gitignore
+++ b/.gitignore
@@ -184,3 +184,4 @@ tests/data/day5.csv
 # Other virtual environments
 .venv-*
 venv-*
+notebooks/test.ipynb
diff --git a/iglu_python/utils.py b/iglu_python/utils.py
index fc304c6..8291bba 100644
--- a/iglu_python/utils.py
+++ b/iglu_python/utils.py
@@ -213,6 +213,8 @@ def CGMS2DayByDay(  # noqa: C901
     if dt0 is None:
         # Use most common time difference (for pandas 1.5.x backward compatibility)
         time_diffs = pd.Series(data.index).diff().dropna()
+        if time_diffs.empty:
+            raise ValueError("Not enough data to calculate time step")
         # Pandas TimedeltaIndex does not have a .mode() method directly.
         # We'll convert to seconds and use pd.Series.mode()
         # Use .dt accessor for pandas 1.5.x compatibility
diff --git a/pyproject.toml b/pyproject.toml
index 0c0ec4b..9130214 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "iglu_python"
-version = "0.4.0"
+version = "0.4.2"
 description = "Python implementation of the iglu package for continuous glucose monitoring data analysis"
 readme = "README.md"
 requires-python = ">=3.11"
@@ -28,7 +28,7 @@ dependencies = [
     "pandas",
     "tzlocal",
     "openpyxl",
-    "matplotlib",
+    "matplotlib"
 ]
 
 [project.urls]
diff --git a/uv.lock b/uv.lock
index 53b5d89..2ef6bf9 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 2
 requires-python = ">=3.11"
 resolution-markers = [
     "python_full_version >= '3.12'",
@@ -621,13 +621,14 @@ wheels = [
 
 [[package]]
 name = "iglu-python"
-version = "0.3.8"
+version = "0.4.2"
 source = { editable = "." }
 dependencies = [
     { name = "matplotlib" },
     { name = "numpy" },
     { name = "openpyxl" },
     { name = "pandas" },
+    { name = "pyarrow" },
     { name = "tzlocal" },
 ]
 
@@ -676,6 +677,7 @@ requires-dist = [
     { name = "pandas" },
     { name = "pre-commit", marker = "extra == 'dev'", specifier = ">=3.0.0" },
     { name = "pre-commit", marker = "extra == 'lint'", specifier = ">=3.0.0" },
+    { name = "pyarrow", specifier = ">=21.0.0" },
     { name = "pyarrow", marker = "extra == 'dev'", specifier = ">=21.0.0" },
     { name = "pytest", marker = "extra == 'dev'", specifier = ">=8.4.2" },
     { name = "pytest", marker = "extra == 'test'", specifier = ">=8.4.2" },