Polishing.

Simplify code. Use putIfAbsent instead of custom check.

[#636][closes #641]

Author: mp911de

src/main/java/io/r2dbc/postgresql/PostgresqlRow.java

@@ -59,9 +59,7 @@ final class PostgresqlRow implements io.r2dbc.postgresql.api.PostgresqlRow {
         this.data = Assert.requireNonNull(data, "data must not be null");
 
         if (metadata instanceof PostgresqlRowMetadata) {
-            this.columnNameIndexCacheMap = Assert.requireNonNull(
-                ((PostgresqlRowMetadata) metadata).getColumnNameIndexMap(),
-                "columnNameIndexCacheMap must not be null");
+            this.columnNameIndexCacheMap = ((PostgresqlRowMetadata) metadata).getColumnNameIndexMap();
         } else {
             this.columnNameIndexCacheMap = createColumnNameIndexMap(this.fields);
         }

src/main/java/io/r2dbc/postgresql/PostgresqlRowMetadata.java

@@ -48,15 +48,13 @@ final class PostgresqlRowMetadata extends AbstractCollection<String> implements
 
     PostgresqlRowMetadata(List<PostgresqlColumnMetadata> columnMetadatas) {
         this.columnMetadatas = Assert.requireNonNull(columnMetadatas, "columnMetadatas must not be null");
-        this.nameKeyedColumns = new LinkedHashMap<>();
+        this.nameKeyedColumns = new LinkedHashMap<>(columnMetadatas.size(), 1);
         this.columnNameIndexMap = new HashMap<>(columnMetadatas.size(), 1);
 
         int i = 0;
         for (PostgresqlColumnMetadata columnMetadata : columnMetadatas) {
-            if (!this.nameKeyedColumns.containsKey(columnMetadata.getName())) {
-                this.nameKeyedColumns.put(columnMetadata.getName(), columnMetadata);
-            }
-            columnNameIndexMap.putIfAbsent(columnMetadata.getName().toLowerCase(Locale.ROOT), i++);
+            this.nameKeyedColumns.putIfAbsent(columnMetadata.getName(), columnMetadata);
+            this.columnNameIndexMap.putIfAbsent(columnMetadata.getName().toLowerCase(Locale.ROOT), i++);
         }
     }