coalesce

Short definition from Wiktionary

Verb

1. 1
   To join into a single mass or whole.
2. 2
   To form from different pieces or elements.
3. 3
   To bond pieces of metal into a continuous whole by liquefying parts of each piece, bringing the liquids into contact, and allowing the combined liquid to solidify.
4. 4
   To merge, to intermingle freely.
5. 5
   To convert a null value to a defined value.