Omission of the indefinite article is before abstract nouns used in a general sense.
Examples of the omission of the indefinite article
Travel completes our education.
Life is grand.
We are very font of music

The Indefinite article omission
Also omission is happened before material nouns used in a general sense.
Examples
Do you take milk in your tea?
The chair is made of wood.
We buy croissants at the baker’s.
Before the names of languages we don’t use article.
Examples
If we put the word language after the name of a language, in that case the definite article is used.
Example:
the German language
the French language
the Italian language
the Greek language
In the following expressions we don’t use articles.
in pencil
by bicycle
to be in trouble
by car
to go home
at home
by bus
to go to bed
…
and so, you got a picture