Remove nulls

[kevinwallimann]

There are many null checks for arguments in the codebase, e.g.

  override def write(dataFrame: DataFrame, streamManager: StreamManager): StreamingQuery = {
    if (dataFrame == null) {
      throw new IllegalArgumentException("Null DataFrame.")
    }

Since null should not be used in scala, an occurrence of null is a serious problem which cannot be handled. Throwing an IllegalArgumentException instead of letting the program fail with a NullPointerException adds little information.

Task

• Remove null checks
• Wrap null values coming from Java code in Option