Fix merge error

import missing package, merge error.

Author: smasala

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -22,6 +22,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.samskivert.mustache.Mustache;
 import com.samskivert.mustache.Mustache.Compiler;
+import com.samskivert.mustache.Mustache.Lambda;
 
 import io.swagger.v3.core.util.Json;
 import io.swagger.v3.oas.models.OpenAPI;