Fix boolean fied validation

Field presence was checked by `if data then` which is false in cases:
1. data = nil - expected
2. data = false - not expected

Closes #88

Author: Khatskevich

avro_schema/frontend.lua

@@ -803,7 +803,7 @@ copy_data = function(schema, data, visited)
             end
             -- copy data
             for _, field in ipairs(schema.fields) do
-                if data[field.name] then
+                if data[field.name] ~= nil then
                     -- a field is present in data
                     ptr = field.name
                     res[field.name] =

test/ddt_suite/validate.lua

@@ -38,6 +38,19 @@ t {
     validate_error = 'Not a boolean: 100500'
 }
 
+-- gh-88, false in record field is treated as absense of value
+t {
+    schema = [[{
+        "type": "record",
+        "name": "X",
+        "fields": [
+            {"name": "f1", "type": "boolean"}
+        ]
+    }]],
+    validate = [[ {"f1": false} ]],
+    validate_only = true
+}
+
 -- int
 
 t {