Fix Element#prepend_to always raising NoMethodError

lib/docx/elements/element.rb

@@ -42,7 +42,8 @@ def append_to(element)
 
       # Insert node as first child (after properties)
       def prepend_to(element)
-        @node = element.node.properties.add_next_sibling(@node)
+        properties = element.properties if element.respond_to?(:properties)
+        @node = properties ? properties.add_next_sibling(@node) : element.node.prepend_child(@node)
         self
       end
 

spec/docx/elements/element_spec.rb

@@ -98,6 +98,36 @@ def texts
     end
   end
 
+  # Regression tests for #189
+  describe '#prepend_to' do
+    let(:run) { element_class.new(w_node('<w:r><w:t>new </w:t></w:r>')) }
+
+    it 'inserts the node right after the properties of a container' do
+      paragraph = Docx::Elements::Containers::Paragraph.new(
+        w_node('<w:p><w:pPr><w:jc w:val="center"/></w:pPr><w:r><w:t>text</w:t></w:r></w:p>')
+      )
+
+      expect(run.prepend_to(paragraph)).to equal(run)
+      expect(paragraph.node.element_children.map(&:name)).to eq(%w[pPr r r])
+      expect(paragraph.text).to eq('new text')
+      expect(run.node.parent).to equal(paragraph.node)
+    end
+
+    it 'inserts the node as the first child of a container without properties' do
+      paragraph = Docx::Elements::Containers::Paragraph.new(w_node('<w:p><w:r><w:t>text</w:t></w:r></w:p>'))
+
+      run.prepend_to(paragraph)
+
+      expect(paragraph.text).to eq('new text')
+    end
+
+    it 'inserts the node as the first child of a non-container element' do
+      run.prepend_to(first)
+
+      expect(texts).to eq(%w[new\ first second])
+    end
+  end
+
   describe '.create_with' do
     it 'builds a detached element from the class tag in the same XML document' do
       created = element_class.create_with(first)