NuGet packages that depend on other NuGet packages should list those packages as dependencies in the .nuspec instead of bundling the dependencies. Bundling it causes can cause problems if a project that uses the NPOI package also uses the DotNetZip package, possibly a different version than is bundled with NPOI. Which DotNetZip dll will be referenced?
If DotNetZip is listed as a package dependency instead, it will be installed when NPOI is installed if it is not installed already, upgraded if it needs to be to meet the version that NPOI depends on, or DotNetZip will be left alone if it is already installed to the project with a version that meets NPOIs dependency.
If DotNetZip is listed as a package dependency instead, it will be installed when NPOI is installed if it is not installed already, upgraded if it needs to be to meet the version that NPOI depends on, or DotNetZip will be left alone if it is already installed to the project with a version that meets NPOIs dependency.