public CreateFormData addFieldsEntry(String key, FieldConfig value) {
        if (null == this.fields) {
            this.fields = new java.util.HashMap<String, FieldConfig>();
        }
        if (this.fields.containsKey(key))
            throw new IllegalArgumentException("Duplicated keys (" + key.toString() + ") are provided.");
        this.fields.put(key, value);
        return this;
    }
Add a single Fields entry

@see CreateFormData#withFields
@returns a reference to this object so that method calls can be chained together.
aws-java-sdk-amplifyuibuilder/src/main/java/com/amazonaws/services/amplifyuibuilder/model/CreateFormData.java