diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a71bf84..198dbd8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -19,16 +19,19 @@ jobs:
       matrix:
         os: [ubuntu-22.04]
         elixir_version: [1.15, 1.16, 1.17]
-        otp_version: [25, 26, 27]
+        otp_version: [ 25, 26, 27]
         exclude:
           - otp_version: 27
             elixir_version: 1.15
           - otp_version: 27
             elixir_version: 1.16
+
     steps:
       - uses: actions/checkout@v4
 
-      - uses: erlef/setup-beam@v1
+      - name: Set up Elixir
+        id: beam
+        uses: erlef/setup-beam@v1
         with:
           otp-version: ${{matrix.otp_version}}
           elixir-version: ${{matrix.elixir_version}}
@@ -44,8 +47,6 @@ jobs:
 
       - run: mix deps.get
 
-      - run: mix format --check-formatted
-
       - run: mix deps.unlock --check-unused
 
       - run: mix deps.compile
@@ -55,3 +56,85 @@ jobs:
       - run: mix credo --strict --format=oneline
 
       - run: mix test --warnings-as-errors --cover
+
+  dialyzer:
+    runs-on: ubuntu-22.04
+    env:
+      MIX_ENV: dev
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Elixir
+        id: beam
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: 1.16
+          otp-version: 26
+
+      - uses: actions/cache@v4
+        with:
+          path: |
+            deps
+            _build
+          key: deps-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            deps-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}
+
+      - run: mix deps.get
+
+      - name: Restore PLT cache
+        id: plt_cache_restore
+        uses: actions/cache/restore@v3
+        with:
+          key: |
+            plts-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            plts-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-
+          path: |
+            priv/plts
+
+      - name: Create PLTs
+        if: steps.plt_cache_restore.outputs.cache-hit != 'true'
+        run: mix dialyzer --plt
+
+      - name: Save PLT cache
+        id: plt_cache_save
+        if: steps.plt_cache_restore.outputs.cache-hit != 'true'
+        uses: actions/cache/save@v3
+        with:
+          key: |
+            plts-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
+          path: |
+            priv/plts
+
+      - name: Run dialyzer
+        run: mix dialyzer --format github --format dialyxir
+
+  check_format:
+    runs-on: ubuntu-22.04
+    env:
+      MIX_ENV: dev
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Elixir
+        id: beam
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: 1.16
+          otp-version: 26
+
+      - uses: actions/cache@v4
+        with:
+          path: |
+            deps
+            _build
+          key: deps-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            deps-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}
+
+      - run: mix deps.get
+
+      - run: mix format --check-formatted
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44950ae..4d98856 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
  # CHANGELOG
 
+## v0.15.1 (2024-12-04)
+
+### Changed
+
+* Fix dialyzer errors
 ## v0.15.0 (2024-10-01)
 
 ### Changed
diff --git a/lib/uinta/formatter/util.ex b/lib/uinta/formatter/util.ex
index 579a016..3fdcebc 100644
--- a/lib/uinta/formatter/util.ex
+++ b/lib/uinta/formatter/util.ex
@@ -59,7 +59,7 @@ defmodule Uinta.Formatter.Util do
   @doc """
   RFC3339 UTC "Zulu" format.
   """
-  @spec format_timestamp(Logger.Formatter.time()) :: String.t()
+  @spec format_timestamp(Types.time()) :: String.t()
   def format_timestamp({date, time}) do
     IO.iodata_to_binary([format_date(date), ?T, format_time(time), ?Z])
   end
diff --git a/lib/uinta/plug.ex b/lib/uinta/plug.ex
index 13a6700..7895cc4 100644
--- a/lib/uinta/plug.ex
+++ b/lib/uinta/plug.ex
@@ -98,7 +98,12 @@ if Code.ensure_loaded?(Plug) do
     @query_name_regex ~r/^\s*(?:query|mutation)\s+(\w+)|{\W+(\w+)\W+?{/m
 
     @type format :: :json | :map | :string
-    @type graphql_info :: %{type: String.t(), operation: String.t(), variables: String.t() | nil}
+    @type graphql_info :: %{
+            type: String.t(),
+            operation: String.t(),
+            variables: String.t(),
+            query: String.t() | nil
+          }
     @type opts :: %{
             level: Logger.level() | {module(), atom(), list()},
             format: format(),
@@ -217,7 +222,7 @@ if Code.ensure_loaded?(Plug) do
       end
     end
 
-    @spec format_line(map(), format()) :: iodata() | map()
+    @spec format_line(map(), format()) :: iodata() | map() | String.t()
     defp format_line(info, :map) do
       format_info(info)
     end
@@ -269,11 +274,11 @@ if Code.ensure_loaded?(Plug) do
 
     @spec query(graphql_info(), opts()) :: String.t() | nil
     defp query(_, %{include_unnamed_queries: false}), do: nil
-    defp query(%{query: query}, _), do: query
+    defp query(%{query: query}, _) when not is_nil(query), do: query
     defp query(_, _), do: nil
 
     @spec variables(graphql_info() | nil) :: String.t() | nil
-    defp variables(%{variables: variables}), do: variables
+    defp variables(%{variables: variables}) when not is_nil(variables), do: variables
     defp variables(_), do: nil
 
     @spec graphql_info(Plug.Conn.t(), opts()) :: graphql_info() | nil
diff --git a/mix.exs b/mix.exs
index 332a156..57adecf 100644
--- a/mix.exs
+++ b/mix.exs
@@ -2,7 +2,7 @@ defmodule Uinta.MixProject do
   use Mix.Project
 
   @project_url "https://github.com/podium/uinta"
-  @version "0.15.0"
+  @version "0.15.1"
 
   def project do
     [