add nil clause for Formatter.get_emoji/1 to return an empty result

lib/pleroma/formatter.ex

@@ -157,6 +157,8 @@ defmodule Pleroma.Formatter do
     end)
   end
 
+  def get_emoji(nil), do: []
+
   def get_emoji(text) do
     Enum.filter(@emoji, fn {emoji, _} -> String.contains?(text, ":#{emoji}:") end)
   end

test/formatter_test.exs

@@ -199,4 +199,14 @@ defmodule Pleroma.FormatterTest do
 
     assert Formatter.get_emoji(text) == [{"moominmamma", "/finmoji/128px/moominmamma-128.png"}]
   end
+
+  test "it returns a nice empty result when no emojis are present" do
+    text = "I love moominamma"
+    assert Formatter.get_emoji(text) == []
+  end
+
+  test "it doesn't die when text is absent" do
+    text = nil
+    assert Formatter.get_emoji(text) == []
+  end
 end