Merge pull request #497 from data-integrations/PLUGIN-520-0.15

[PLUGIN-520] Cherry Pick into 0.15

Author: fernst

src/main/java/io/cdap/plugin/gcp/bigtable/source/BigtableSourceConfig.java

@@ -89,7 +89,6 @@ public final class BigtableSourceConfig extends GCPReferenceSourceConfig {
   @Description("Mappings from Bigtable column name to record field. " +
     "Column names must be formatted as <family>:<qualifier>.")
   @Macro
-  @Nullable
   final String columnMappings;
 
   @Name(SCAN_ROW_START)