hugegraph-loader/src/main/java/org/apache/hugegraph/loader/mapping/ElementMapping.java [75:93]:
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    public void check() throws IllegalArgumentException {
        E.checkArgument(this.label != null && !this.label.isEmpty(),
                        "The label can't be null or empty");
        E.checkArgument(this.selectedFields.isEmpty() ||
                        this.ignoredFields.isEmpty(),
                        "Not allowed to specify selected(%s) and ignored(%s) " +
                        "fields at the same time, at least one of them " +
                        "must be empty", selectedFields, ignoredFields);
        this.mappingFields.values().forEach(value -> {
            E.checkArgument(value != null,
                            "The value in field_mapping can't be null");
        });
        this.mappingValues.values().forEach(m -> {
            m.values().forEach(value -> {
                E.checkArgument(value != null,
                                "The value in value_mapping can't be null");
            });
        });
    }
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hugegraph-loader/src/main/java/org/apache/hugegraph/loader/struct/ElementStructV1.java [101:119]:
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    public void check() throws IllegalArgumentException {
        E.checkArgument(this.label != null && !this.label.isEmpty(),
                        "The label can't be null or empty");
        E.checkArgument(this.selectedFields.isEmpty() ||
                        this.ignoredFields.isEmpty(),
                        "Not allowed to specify selected(%s) and ignored(%s) " +
                        "fields at the same time, at least one of them " +
                        "must be empty", selectedFields, ignoredFields);
        this.mappingFields.values().forEach(value -> {
            E.checkArgument(value != null,
                            "The value in field_mapping can't be null");
        });
        this.mappingValues.values().forEach(m -> {
            m.values().forEach(value -> {
                E.checkArgument(value != null,
                                "The value in value_mapping can't be null");
            });
        });
    }
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