raise if docuemtn select result is nil. maybe its invalid.

lib/docx_templater.rb

@@ -1,4 +1,8 @@
 module DocxTemplater
+  # Some docx, such as generated by non-microsoft word, sometime make invalid docx. Its input stream returns Zip::NullInputStream. When it detected, this error is raised.
+  InvalidInputError = Class.new(StandardError)
+
+
   module_function
 
   def log(str)

lib/docx_templater/docx_creator.rb

@@ -5,8 +5,6 @@
 module DocxTemplater
   class DocxCreator
     attr_reader :template_path, :template_processor
-    # Some docx, such as generated by non-microsoft word, sometime make invalid docx. Its input stream returns Zip::NullInputStream. When it detected, this error is raised.
-    InvalidInputError = Class.new(StandardError)
 
     def initialize(template_path, data, escape_html = true)
       @template_path = template_path
@@ -25,7 +23,7 @@ def generate_docx_bytes
           entry_name = entry.name
           out.put_next_entry(entry_name)
           if entry.get_input_stream.is_a?(Zip::NullInputStream)
-            raise InvalidInputError
+            raise ::DocxTemplater::InvalidInputError, "stream is Zip::NullInputStream"
           end
           out.write(copy_or_template(entry_name, entry.get_input_stream.read))
         end

lib/docx_templater/template_processor.rb

@@ -22,6 +22,12 @@ def self.scan_params template_path
       document = Zip::File.open(template_path)
                    .select { |entry| entry.name == DOCUMENT_XML }
                    .first
+
+      unless document
+        raise ::DocxTemplater::InvalidInputError, "There is no entry matching to #{DOCUMENT_XML}"
+      end
+
+      document = document
                    .get_input_stream
                    .read
       document.force_encoding(Encoding::UTF_8) if document.respond_to?(:force_encoding)